Add transcription support for single agent live scenario for Java ADK

[jinnigu]

** Please make sure you read the contribution guide and file the issues in the right place. **
Contribution guide.

Is your feature request related to a problem? Please describe.
Currently, Java ADK live enable audio transcription only for multi-agent scenarios (https://github.com/google/adk-java/blob/main/core/src/main/java/com/google/adk/runner/Runner.java#L400). For single agent voice use case, the audio transcription will provide a persistent record, which is useful for debugging or history search.

Similar pending PR to support Python ADK transcription for single agent live scenario (google/adk-python#3259).

Describe the solution you'd like
Enable transcription for single-agent live scenarios, not just multi-agent live scenarios.

Describe alternatives you've considered
Users can manually config.

Additional context
I will raise a PR and add tutorial.

[Pratapchandradeo]

Hey @jinnigu, I'd like to work on this issue. Perfect first contribution for me to dive into the ADK codebase.
I'll start looking at the multi-agent implementation and follow the same pattern.

[jinnigu]

Hey @jinnigu, I'd like to work on this issue. Perfect first contribution for me to dive into the ADK codebase. I'll start looking at the multi-agent implementation and follow the same pattern.

Hi @Pratapchandradeo

As I have already prepared a PR with tutorial and tests, do you mind help contribute to some other issues? Thank you!

[jinnigu]

PR ready for review: #556

[jinnigu]

#556 has been merged. Close this issue.