feat(otel): add --otel_to_cloud experimental support

Cloud Trace, Cloud Monitoring and Cloud Logging integrations are set up via OTel if otel_to_cloud CLI param/fast_api arg is provided.

This is similar to current Cloud Trace integration via trace_to_cloud, just extended to Monitoring and Logging as well.

PiperOrigin-RevId: 807385680

tests/unittests/flows/llm_flows/test_tool_telemetry.py

@@ -17,10 +17,10 @@ from typing import Dict
 from typing import Optional
 from unittest import mock
 
-from google.adk import telemetry
 from google.adk.agents.llm_agent import Agent
 from google.adk.events.event import Event
 from google.adk.flows.llm_flows.functions import handle_function_calls_async
+from google.adk.telemetry import tracing
 from google.adk.tools.function_tool import FunctionTool
 from google.genai import types
 
@@ -65,7 +65,7 @@ async def test_simple_function_with_mocked_tracer(monkeypatch):
   mock_start_as_current_span_func.return_value = returned_context_manager_mock
 
   monkeypatch.setattr(
-      telemetry.tracer, 'start_as_current_span', mock_start_as_current_span_func
+      tracing.tracer, 'start_as_current_span', mock_start_as_current_span_func
   )
 
   mock_adk_trace_tool_call = mock.Mock()