chore: bidi streaming example on run live fast api

This sample connects to adk agent api server with websocket, to exchange streaming audio/text.

PiperOrigin-RevId: 805531120

contributing/samples/live_agent_api_server_example/readme.md

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+# What's this?
+
+This is a sample that shows how to start the ADK api server, and how to connect
+your agents in a live(bidi-stremaing) way. It works text and audio input, and
+the response is always audio.
+
+## Prerequisite
+
+- Make sure you go through https://google.github.io/adk-docs/streaming/
+
+## Instruction for this sample
+
+- The audio libraries we used here doesn't have noise cancellation. So the noise
+ may feed back to the model. You can use headset to avoid this or tune down
+  voice volume, or implement your own noise cancellation logic.
+- Please ensure you grant the right mic/sound device permission to the terminal
+ that runs the script. Sometimes, terminal inside VSCode etc dones't really work
+  well. So try native terminals if you have permission issue.
+- start api server first for your agent folder. For example, my anents are
+ locoated in contributing/samples. So I will run
+  `adk api_server contributing/samples/`. Keep this running.
+- then in a separate window, run `python3 live_agent_example.py`
+
+## Misc
+
+- Provide a few pre-recorded audio files for testing.