Implement initial OTel setup for ADK agents

[krisztianfekete]

This PR lets you enable ADK's built-in instrumentation and specify an otlp endpoint where you can push tracing data.

Example output from an instrumented agent:

Span #2
    Trace ID       : e5091e6a8908770a95bf5ed73b852e29
    Parent ID      : 3e7bbdb443a54eff
    ID             : 8ea357d47f0058c1
    Name           : call_llm
    Kind           : Internal
    Start time     : 2026-01-14 16:53:18.36083154 +0000 UTC
    End time       : 2026-01-14 16:53:19.579240184 +0000 UTC
    Status code    : Unset
    Status message :
    DroppedAttributesCount: 0
    DroppedEventsCount: 0
    DroppedLinksCount: 0
Attributes:
     -> gen_ai.system: Str(gcp.vertex.agent)
     -> gen_ai.request.model: Str(openai/gpt-4)
     -> gcp.vertex.agent.invocation_id: Str(e-f3aeaf51-6172-4ee4-9c69-5977fca52be4)
     -> gcp.vertex.agent.session_id: Str(ctx-4fa656b9-5bc8-4a55-b530-1c5ff1218369)
     -> gcp.vertex.agent.event_id: Str(f8bc6371-66c1-45ac-ba7d-9bb45115c1b1)
     -> gcp.vertex.agent.llm_request: Str({"model": "openai/gpt-4", "config": {"system_instruction": "\nYou roll dice and answer questions about the outcome of the dice rolls.\nYou can roll dice of different sizes.\nYou can use multiple tools in parallel by calling functions in parallel (in one request and in one round).\nIt is ok to discuss previous dice roles, and comment on the dice rolls.\nWhen you are asked to roll a die, you must call the roll_die tool with the number of sides. Be sure to pass in an integer. Do not pass in a string.\nYou should never roll a die on your own.\nWhen checking prime numbers, call the check_prime tool with a list of integers. Be sure to pass in a list of integers. You should never pass in a string.\nYou should not check prime numbers before calling the tool.\nWhen you are asked to roll a die and check prime numbers, you should always make the following two function calls:\n1. You should first call the roll_die tool to get a roll. Wait for the function response before calling the check_prime tool.\n2. After you get the function response from roll_die tool, you should call the check_prime tool with the roll_die result.\n2.1 If user asks you to check primes based on previous rolls, make sure you include the previous rolls in the list.\n3. When you respond, you must include the roll_die result from step 1.\nYou should always perform the previous 3 steps when asking for a roll and checking prime numbers.\nYou should not rely on the previous history on prime results.\n\n\n    \n\nYou are an agent. Your internal name is \"testagent_agent\".\n\n The description about you is \"testagent agent.\"", "tools": [{"function_declarations": [{"name": "roll_die", "parameters": {"properties": {"sides": {"type": "INTEGER"}}, "required": ["sides"], "type": "OBJECT"}}, {"name": "check_prime", "parameters": {"properties": {"nums": {"items": {"type": "INTEGER"}, "type": "ARRAY"}}, "required": ["nums"], "type": "OBJECT"}}]}], "labels": {"adk_agent_name": "testagent_agent"}}, "contents": [{"parts": [{"text": "roll a dice"}], "role": "user"}, {"parts": [{"function_call": {"id": "call_74woxaXXP1F568UBe38QBVMe", "args": {"sides": 6}, "name": "roll_die"}}], "role": "model"}, {"parts": [{"function_response": {"id": "call_74woxaXXP1F568UBe38QBVMe", "name": "roll_die", "response": {"result": 3}}}], "role": "user"}]})
     -> gcp.vertex.agent.llm_response: Str({"content":{"parts":[{"text":"I rolled a 6-sided die, and the result is 3."}],"role":"model"},"partial":false,"usage_metadata":{"candidates_token_count":16,"prompt_token_count":412,"total_token_count":428}})
     -> gen_ai.usage.input_tokens: Int(412)
     -> gen_ai.usage.output_tokens: Int(16)
Span #3
    Trace ID       : e5091e6a8908770a95bf5ed73b852e29
    Parent ID      : 4afadb631b31a6fb
    ID             : 3e7bbdb443a54eff
    Name           : invoke_agent testagent_agent
    Kind           : Internal
    Start time     : 2026-01-14 16:53:16.961428433 +0000 UTC
    End time       : 2026-01-14 16:53:19.579316392 +0000 UTC
    Status code    : Unset
    Status message :
    DroppedAttributesCount: 0
    DroppedEventsCount: 0
    DroppedLinksCount: 0
Attributes:
     -> gen_ai.operation.name: Str(invoke_agent)
     -> gen_ai.agent.description: Str(testagent agent.)
     -> gen_ai.agent.name: Str(testagent_agent)
     -> gen_ai.conversation.id: Str(ctx-4fa656b9-5bc8-4a55-b530-1c5ff1218369)
Span #4
    Trace ID       : e5091e6a8908770a95bf5ed73b852e29
    Parent ID      : fc71e0b4a7043e64
    ID             : 4afadb631b31a6fb
    Name           : invocation
    Kind           : Internal
    Start time     : 2026-01-14 16:53:16.961243435 +0000 UTC
    End time       : 2026-01-14 16:53:19.57933835 +0000 UTC
    Status code    : Unset
    Status message :
    DroppedAttributesCount: 0
    DroppedEventsCount: 0
    DroppedLinksCount: 0
        {"resource": {"service.instance.id": "76f643d2-7d3f-4029-83da-bf0f9e7d1c37", "service.name": "otelcol", "service.version": "0.143.1"}, "otelcol.component.id": "debug", "otelcol.component.kind": "exporter", "otelcol.signal": "traces"}