fix: make telemetry optional for agents

there is a lot of code in the agents API using the telemetry API and its helpers without checking if that API is even enabled.

This is the only API besides inference actively using telemetry code, so after this telemetry can be optional for the entire stack

Signed-off-by: Charlie Doern <cdoern@redhat.com>

llama_stack/providers/registry/agents.py

@@ -36,6 +36,9 @@ def available_providers() -> list[ProviderSpec]:
                 Api.tool_runtime,
                 Api.tool_groups,
             ],
+            optional_api_dependencies=[
+                Api.telemetry,
+            ],
             description="Meta's reference implementation of an agent system that can use tools, access vector databases, and perform complex reasoning tasks.",
         ),
     ]