Add support for Micrometer tracing

[mhalbritter]

Extracted from #29666

• Support for Micrometer Tracing - you can check out more here https://micrometer.io/docs/tracing

Micrometer Tracing comes with the following features

• Abstraction over a Tracer (Tracer is a library handling a lifecycle of a span. Span is wrapping an action that we would like to measure. Span contains information such as timing, span id - unique identifier for an action, trace id - same identifier for all actions within the same business transaction)
• Tracer bridges. We're bridging from the abstraction to a concrete tracer implementation. We support the following tracers
  • Brave
  • OpenTelemetry (OTel)
• TracingObservationHandler interface and its implementations
• Span exporters /reporters (to visualize latency we should send spans to a reporting system such as Wavefront)
  • Zipkin with Brave
  • Anything that OTel provides out of the box (Zipkin, OTLP etc.)
  • Wavefront with Brave and OTel

We need Boot to configure the Bridges with all of their features.

[mhalbritter]

Base infrastructure

• A lot of the auto-configurations can be used from Spring Cloud Sleuth: brave and otel
• We need to create a Micrometer DefaultTracingObservationHandler bean
  • This will get picked up by the auto-configuration from Add auto-configuration for Micrometer 2.0 Observation API #29666
• This needs a Micrometer Tracer. There are two tracer implementations shipped with Micrometer, BraveTracer and OtelTracer

Brave

• Code in micrometer
• To create a Micrometer BraveTracer, we need a brave Tracer and some other stuff, which all needs Brave Tracing
• Tracing can be customized with some options like the local service name, etc. The reported spans are handled by brave SpanHandlers.

Brave & Zipkin

Zipkin is implemented as a Brave SpanHandler

var sender = URLConnectionSender.create("http://127.0.0.1:9411/api/v2/spans");
var spanReporter = AsyncReporter.builder(sender).build();
var spanHandler = new ZipkinSpanHandler.newBuilder(spanReporter).alwaysReportSpans(true).build();

I guess there are a lot more of the sender implementations.

Brave & Wavefront

• Wavefront is implemented as a brave SpanHandler, see here

Open Telemetry

• Code in micrometer
• TODO

Open Telemetry & Wavefront

• Wavefront is implemented a a otel SpanExporter, see here