Send mqtt message when motion is detected (#3152)

* Send mqtt message when motion is detected

* Use object processing instead of passing mqtt client around

* Cleanup

* Formatting

* add comment

* Make off delay configurable.

* Handle updating each camera based on config off delay

* Formatting

* Update docker-compose.yml

* Fix processing issue

* Update mqtt docs

* Update main config docs

* Make sure multiple True values aren't published for the same motion

* Make sure multiple True values aren't published for the same motion

* Update payload to fit existing HA standard values

* Update docs to fit new values

* Update docs

* Update motion topic

* Use datetime.datetime and remove unused imports

* Cast to int

* Clarify motion detector behavior in docs

* Fix typo

Co-authored-by: Blake Blackshear <blakeb@blakeshome.com>

docs/docs/configuration/index.md

@@ -246,12 +246,14 @@ motion:
   # Enables dynamic contrast improvement. This should help improve night detections at the cost of making motion detection more sensitive
   # for daytime.
   improve_contrast: False
+  # Optional: Delay when updating camera motion through MQTT from ON -> OFF (default: shown below).
+  mqtt_off_delay: 30
 
 # Optional: Record configuration
 # NOTE: Can be overridden at the camera level
 record:
   # Optional: Enable recording (default: shown below)
-  # WARNING: If recording is disabled in the config, turning it on via 
+  # WARNING: If recording is disabled in the config, turning it on via
   #          the UI or MQTT later will have no effect.
   # WARNING: Frigate does not currently support limiting recordings based
   #          on available disk space automatically. If using recordings,