docs(collector): update internal telemetry RPC metrics

Align the internal telemetry docs with the RPC metrics emitted by newer
Collector builds that use the updated Go semantic conventions.

Rename the documented RPC duration metrics to rpc.client.call.duration
and rpc.server.call.duration, remove the deprecated *_per_rpc entries
from the detailed metrics list, and note that older Collector releases
may still expose the legacy rpc.client.duration and rpc.server.duration
metric names.

Author: dol

content/en/docs/collector/internal-telemetry.md

@@ -370,12 +370,14 @@ With this configuration, `otelcol_process_uptime_seconds_total` is exported as
 names used dots (`.`). Prior to Collector v0.120.0, internal metrics exposed
 with Prometheus changed dots (`.`) to underscores (`_`) to match Prometheus
 naming conventions, resulting in metric names that looked like
-`rpc_server_duration`.
+`rpc_server_call_duration`.
 
 Versions 0.120.0 and later of the Collector use Prometheus 3.0 scrapers, so the
 original `http*` and `rpc*` metric names with dots are preserved. The
 [internal metrics](#lists-of-internal-metrics) on this page are listed in their
-original form, such as`rpc.server.duration`. For more information, see the
+original form, such as `rpc.server.call.duration`. Because these metrics come
+from instrumentation libraries, their names can change as the underlying
+semantic conventions evolve. For more information, see the
 [Collector v0.120.0 release notes](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/CHANGELOG.md#v01200).
 
 ### Lists of internal metrics
@@ -453,30 +455,30 @@ files in the repository.
 
 #### Additional `detailed`-level metrics
 
-| Metric name                                           | Description                                                                               | Type      |
-| ----------------------------------------------------- | ----------------------------------------------------------------------------------------- | --------- |
-| `http.client.request.body.size`                       | Measures the size of HTTP client request bodies.                                          | Counter   |
-| `http.client.request.duration`                        | Measures the duration of HTTP client requests.                                            | Histogram |
-| `http.server.request.body.size`                       | Measures the size of HTTP server request bodies.                                          | Counter   |
-| `http.server.request.duration`                        | Measures the duration of HTTP server requests.                                            | Histogram |
-| `http.server.response.body.size`                      | Measures the size of HTTP server response bodies.                                         | Counter   |
-| `otelcol_processor_batch_batch_`<br>`send_size_bytes` | Number of bytes in the batch that was sent.                                               | Histogram |
-| `rpc.client.duration`                                 | Measures the duration of outbound RPC.                                                    | Histogram |
-| `rpc.client.request.size`                             | Measures the size of RPC request messages (uncompressed).                                 | Histogram |
-| `rpc.client.requests_per_rpc`                         | Measures the number of messages received per RPC. Should be 1 for all non-streaming RPCs. | Histogram |
-| `rpc.client.response.size`                            | Measures the size of RPC response messages (uncompressed).                                | Histogram |
-| `rpc.client.responses_per_rpc`                        | Measures the number of messages sent per RPC. Should be 1 for all non-streaming RPCs.     | Histogram |
-| `rpc.server.duration`                                 | Measures the duration of inbound RPC.                                                     | Histogram |
-| `rpc.server.request.size`                             | Measures the size of RPC request messages (uncompressed).                                 | Histogram |
-| `rpc.server.requests_per_rpc`                         | Measures the number of messages received per RPC. Should be 1 for all non-streaming RPCs. | Histogram |
-| `rpc.server.response.size`                            | Measures the size of RPC response messages (uncompressed).                                | Histogram |
-| `rpc.server.responses_per_rpc`                        | Measures the number of messages sent per RPC. Should be 1 for all non-streaming RPCs.     | Histogram |
+| Metric name                                           | Description                                                     | Type      |
+| ----------------------------------------------------- | --------------------------------------------------------------- | --------- |
+| `http.client.request.body.size`                       | Measures the size of HTTP client request bodies.                | Counter   |
+| `http.client.request.duration`                        | Measures the duration of HTTP client requests.                  | Histogram |
+| `http.server.request.body.size`                       | Measures the size of HTTP server request bodies.                | Counter   |
+| `http.server.request.duration`                        | Measures the duration of HTTP server requests.                  | Histogram |
+| `http.server.response.body.size`                      | Measures the size of HTTP server response bodies.               | Counter   |
+| `otelcol_processor_batch_batch_`<br>`send_size_bytes` | Number of bytes in the batch that was sent.                     | Histogram |
+| `rpc.client.call.duration`                            | Measures the duration of outbound remote procedure calls (RPC). | Histogram |
+| `rpc.client.request.size`                             | Measures the size of RPC request messages (uncompressed).       | Histogram |
+| `rpc.client.response.size`                            | Measures the size of RPC response messages (uncompressed).      | Histogram |
+| `rpc.server.call.duration`                            | Measures the duration of inbound remote procedure calls (RPC).  | Histogram |
+| `rpc.server.request.size`                             | Measures the size of RPC request messages (uncompressed).       | Histogram |
+| `rpc.server.response.size`                            | Measures the size of RPC response messages (uncompressed).      | Histogram |
 
 > [!NOTE]
 >
 > The `http*` and `rpc*` metrics are not covered by the maturity levels below
 > since they are not under the Collector SIG control.
 >
+> RPC metric names are version-dependent. Newer Collector releases expose
+> `rpc.client.call.duration` and `rpc.server.call.duration`. Older releases may
+> still expose `rpc.client.duration` and `rpc.server.duration`.
+>
 > The `otelcol_processor_batch_` metrics are unique to the `batchprocessor`.
 >
 > The `otelcol_receiver_`, `otelcol_scraper_`, `otelcol_processor_`, and