Make clearer the distinction between "storage-mode" and "delta-mode" usage of *Settings objects

- Storage mode: for use in `self._settings`. All fields should be specified, i.e. should not be `NOT_GIVEN`.
- Delta mode: for use in `*UpdateSettingsFrame`.

In service of this, this commit:
- Adds a runtime check that all fields are specified in storage mode
- Updates all services to specify all fields in stored settings
- Updates all services to no longer check for `is_given` in stored settings (not necessary anymore)
- Updates relevant docstrings
- Renames `update` to `delta` in `*UpdateSettingsFrame`
- Updates community integrations guide

examples/foundational/55s-update-settings-google-http-tts.py

@@ -99,7 +99,7 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
         await asyncio.sleep(10)
         logger.info("Updating Google HTTP TTS settings: speaking_rate=1.4")
         await task.queue_frame(
-            TTSUpdateSettingsFrame(update=GoogleHttpTTSSettings(speaking_rate=1.4))
+            TTSUpdateSettingsFrame(delta=GoogleHttpTTSSettings(speaking_rate=1.4))
         )
 
     @transport.event_handler("on_client_disconnected")