Improve trace searchability by adding attributes on agent_run span

[alphinside]

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Contribution guide.

Is your feature request related to a problem? Please describe.
Currently if we want to search trace specific to a combination of user id, app nam, or session id. It's hard to find it. The only way to search it is by session id but it's only applicable on call_llm or tool call. It will be helpful if we can find the agent_run trace quickly instead of finding the call_llm first, then find the parents.

The image above show searchable attribute on cloud trace on call_llm

The image above show searchable attributes on cloud trace on agent_run ( only 1 attribute )

Describe the solution you'd like
Add core run attribute to be searchable in agent_run span : session_id, app_name, user_id, invocation_id

Describe alternatives you've considered
None ATM

Additional context
On ADK v1.2.1

[alphinside]

trying to implement trace_agent_run in telemetry.py to be used in base_agent.py, encountered circular import due to InvocationContext is imported inside telemetry, where as InvocationContext in invocation_context.py is also importing BaseAgent from base_agent.py