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

src/pipecat/services/lmnt/tts.py

@@ -206,16 +206,16 @@ class LmntTTSService(InterruptibleTTSService):
 
         await self._disconnect_websocket()
 
-    async def _update_settings(self, update: TTSSettings) -> dict[str, Any]:
-        """Apply a settings update.
+    async def _update_settings(self, delta: TTSSettings) -> dict[str, Any]:
+        """Apply a settings delta.
 
         Args:
-            update: A :class:`TTSSettings` (or ``LmntTTSSettings``) delta.
+            delta: A :class:`TTSSettings` (or ``LmntTTSSettings``) delta.
 
         Returns:
             Dict mapping changed field names to their previous values.
         """
-        changed = await super()._update_settings(update)
+        changed = await super()._update_settings(delta)
 
         if changed:
             await self._disconnect()