Support gemini audioStreamEnd for realtimeInput

[chanhohang]

The current gemini_llm_connection send_realtime support ActivityStart and ActivityEnd, it's great if it also support audioStreamEnd from gemini live api to force flush audio with VAD enabled.

[klateefa]

@chanhohang Thank you for reporting this. I understand the request is currently under review. Please keep me posted if anything else is needed. Thanks for your patience.

[Yashas1600]

Put together a fix in #6442.

[guptaishaan]

Took a look, #6508 should address it.