Found docs updates needed from ADK python release v1.14.0 to v1.14.1

[xuanyang15]

I have analyzed the changes between ADK Python releases v1.14.0 and v1.14.1 and identified several documentation updates. Here are the instructions on how to update the ADK docs:

1. Add documentation for the new Spanner similarity_search tool.
   A new tool similarity_search has been added to the Spanner toolset. This tool allows users to perform vector similarity searches in Spanner.

   Proposed Change:
   Add a new section for the Spanner toolset in docs/tools/built-in-tools.md and document the similarity_search tool. The documentation should include a description of the tool, its parameters, and an example of how to use it.

   Reasoning:
   This is a new feature that needs to be documented to make users aware of its existence and to guide them on how to use it.

   Reference:

   • Code change: google/adk-python@22822a5
   • Code file: src/google/adk/tools/spanner/search_tool.py

2. Update the BigQuery tool documentation to include the location parameter.
   The BigQuery toolset now supports a location parameter that allows users to specify the BigQuery location.

   Proposed Change:
   Update the BigQuery tool documentation in docs/tools/built-in-tools.md to include the location parameter in the BigQueryToolset configuration.

   Reasoning:
   This is a new feature that needs to be documented to make users aware of its existence and to guide them on how to use it.

   Reference:

   • Code change: google/adk-python@22822a5
   • Code file: src/google/adk/tools/bigquery/config.py

3. Add a new section for the live agent API server example.
   A new example has been added to demonstrate how to use the live agent API server with audio.

   Proposed Change:
   Add a new bullet point to the "Custom Audio Streaming app sample" section in docs/streaming/index.md with a link to the new example.

   Reasoning:
   This is a new example that needs to be documented to make users aware of its existence and to guide them on how to use it.

   Reference:

   • Code change: google/adk-python@22822a5
   • Code file: contributing/samples/live_agent_api_server_example/readme.md

4. Update the A2A documentation to reflect the logging improvements.
   The A2A logging has been improved to provide more detailed information.

   Proposed Change:
   Update the A2A documentation in docs/a2a/index.md to reflect the logging improvements.

   Reasoning:
   This is an improvement that needs to be documented to make users aware of the new logging capabilities.

   Reference:

   • Code change: google/adk-python@22822a5
   • Code file: src/google/adk/a2a/logs/log_utils.py