Add an entity service for saving nest event related snapshots (#58369)

* Add an entity service for saving nest event related snapshots

Add an entity service `nest.snapshot_event` for recording camera event
related media to disk. This is based on `camera.snapshot` but takes in
a parameter for a Nest API event_id.

PR #58299 adds `nest_event_id` to events published by nest so that they can
be hooked up to this service for capturing events.

Future related work includes:
- Height & Width parameters for the rendered image
- Support video clips for new battery cameras
- An API for proxying media related to events, separate from the camera image thumbnail
- A Nest MediaSource for browsing media related to events

* Revert debugging information

* Add test coverage for OSError failure case

* Add service description for nest snapshot service

* Reduce unnecessary diffs.

* Sort nest camera imports

* Remove unnecessary if block in snapshot

homeassistant/components/nest/const.py

@@ -22,3 +22,5 @@ SDM_SCOPES = [
 ]
 API_URL = "https://smartdevicemanagement.googleapis.com/v1"
 OOB_REDIRECT_URI = "urn:ietf:wg:oauth:2.0:oob"
+
+SERVICE_SNAPSHOT_EVENT = "snapshot_event"