Output only satellite - part 2 (#278)

Introduce a new `--output-only` command-line flag and corresponding `ENABLE_OUTPUT_ONLY` environment variable. This allows users to run the assistant in output-only mode, where it only supports announcements. The change includes updates to configuration examples, documentation, and the Docker entrypoint script.

README.md

@@ -79,6 +79,7 @@ usage: __main__.py [-h] [--name NAME] [--audio-input-device AUDIO_INPUT_DEVICE]
 | `--port` | Port for ESPHome server | 6053 |
 | `--enable-thinking-sound` | Enable thinking sound on startup | False |
 | `--debug` | Print DEBUG messages to console | False |
+| `--output-only` | Enable output only mode | False |
 
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