LPR improvements (#17289)

* config options

* processing in maintainer

* detect and process dedicated lpr plates

* create camera type, add manual event and save snapshot

* use const

* ensure lpr events are always detections, typing fixes

* docs

* docs tweaks

* add preprocessing and penalization for low confidence chars

frigate/comms/detections_updater.py

@@ -11,6 +11,7 @@ class DetectionTypeEnum(str, Enum):
     api = "api"
     video = "video"
     audio = "audio"
+    lpr = "lpr"
 
 
 class DetectionPublisher(Publisher):

frigate/comms/event_metadata_updater.py

@@ -15,6 +15,8 @@ class EventMetadataTypeEnum(str, Enum):
     regenerate_description = "regenerate_description"
     sub_label = "sub_label"
     recognized_license_plate = "recognized_license_plate"
+    lpr_event_create = "lpr_event_create"
+    save_lpr_snapshot = "save_lpr_snapshot"
 
 
 class EventMetadataPublisher(Publisher):