Enhance observability in Google ADK and Langchain

[notgitika]

Description

Observability should be enabled by default in new projects so users get monitoring and tracing out of the box without needing to configure it manually.

Category

Feature Request

Acceptance Criteria

• New projects created with agentcore create have observability enabled by default
• Users can opt out of observability if desired
• Documentation reflects the default-on behavior

[tejaskash]

I think this is already enabled, we need to get someone familiar with Obs to test it out and confirm

[notgitika]

Verification update: LangChain is not a remaining issue. The current template includes the AWS OpenTelemetry distro and explicit LangChain instrumentation from #552, #835, and #836. A live deployed invocation completed a tool call and emitted 22 spans, including invoke_agent, chat, execute_task, and execute_tool. The remaining defect is specific to the Google ADK templates and is addressed by #1773.