Validate and normalize instance state configuration

Adds validation for the `aws_ec2_instance_states` configuration to
ensure only valid EC2 instance state names are used. The validation
filters out invalid states and logs a warning, allowing the node to
start with the valid states.

The `validate_instance_states/1` function checks each configured state
against the list of valid EC2 instance states defined in the
`?VALID_EC2_INSTANCE_STATES` macro. Invalid states are discarded and
logged as a warning.

The `normalize_state/1` function handles both atom and string inputs,
converting atoms to strings for consistent handling. This supports
configuration via `advanced.config` with atoms (`[running, pending]`)
or via `rabbitmq.conf` with strings (`["running", "pending"]`).

Tests verify validation works correctly for:
- All valid states (strings)
- Mixed valid and invalid states (filters out invalid)
- Atom inputs (normalizes to strings)
- Mixed valid and invalid atoms

(cherry picked from commit 41d5030)

Author: lukebakken

deps/rabbitmq_peer_discovery_aws/src/rabbit_peer_discovery_aws.erl

@@ -30,6 +30,8 @@
 
 -define(BACKEND_CONFIG_KEY, peer_discovery_aws).
 
+-define(VALID_EC2_INSTANCE_STATES, ["pending", "running", "shutting-down", "terminated", "stopping", "stopped"]).
+
 -define(CONFIG_MAPPING,
          #{
           aws_autoscaling                    => #peer_discovery_config_entry_meta{
@@ -321,9 +323,32 @@ maybe_add_instance_state_filters(QArgs, Num) ->
         [] ->
             QArgs;
         [_|_] ->
-            add_instance_state_filters(States, QArgs, Num)
+            ValidStates = validate_instance_states(States),
+            add_instance_state_filters(ValidStates, QArgs, Num)
     end.
 
+-spec validate_instance_states(list()) -> list().
+validate_instance_states(States) ->
+    NormalizedStates = [normalize_state(State) || State <- States],
+    {Valid, Invalid} = lists:partition(
+        fun(State) -> lists:member(State, ?VALID_EC2_INSTANCE_STATES) end,
+        NormalizedStates),
+    case Invalid of
+        [] ->
+            ok;
+        [_|_] ->
+            rabbit_log:warning(
+                "Ignoring invalid EC2 instance states in configuration: ~tp. "
+                "Valid states are: ~tp", [Invalid, ?VALID_EC2_INSTANCE_STATES])
+    end,
+    Valid.
+
+-spec normalize_state(atom() | string()) -> string().
+normalize_state(State) when is_atom(State) ->
+    atom_to_list(State);
+normalize_state(State) when is_list(State) ->
+    State.
+
 -spec add_instance_state_filters(list(), filters(), integer()) -> filters().
 add_instance_state_filters(States, QArgs, Num) ->
     FilterName = {"Filter." ++ integer_to_list(Num) ++ ".Name", "instance-state-name"},

deps/rabbitmq_peer_discovery_aws/test/unit_SUITE.erl

@@ -23,6 +23,7 @@ groups() ->
      {unit, [], [
                  maybe_add_tag_filters,
                  maybe_add_instance_state_filters,
+                 validate_instance_states,
                  get_hostname_name_from_reservation_set,
                  registration_support,
                  network_interface_sorting,
@@ -64,6 +65,14 @@ maybe_add_instance_state_filters(_Config) ->
     ?assertEqual(Expectation, Result),
     application:unset_env(rabbit, cluster_formation).
 
+validate_instance_states(_Config) ->
+    ValidStates = ["pending", "running", "shutting-down", "terminated", "stopping", "stopped"],
+    ?assertEqual(ValidStates, rabbit_peer_discovery_aws:validate_instance_states(ValidStates)),
+    ?assertEqual(["running"], rabbit_peer_discovery_aws:validate_instance_states(["running", "invalid"])),
+    ?assertEqual([], rabbit_peer_discovery_aws:validate_instance_states(["bogus", "invalid"])),
+    ?assertEqual(["running", "pending"], rabbit_peer_discovery_aws:validate_instance_states([running, pending])),
+    ?assertEqual(["running"], rabbit_peer_discovery_aws:validate_instance_states([running, invalid])).
+
 get_hostname_name_from_reservation_set(_Config) ->
     ok = eunit:test({
       foreach,