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/55zo-update-settings-grok-realtime.py

@@ -101,7 +101,7 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
         logger.info("Updating Grok Realtime LLM settings: voice='Rex'")
         await task.queue_frame(
             LLMUpdateSettingsFrame(
-                update=GrokRealtimeLLMSettings(
+                delta=GrokRealtimeLLMSettings(
                     session_properties=events.SessionProperties(voice="Rex")
                 )
             )