Implement support for no recordings indicator on timeline (#18363)

* Indicate no recordings on the history timeline with gray hash marks

This commit includes a new backend API endpoint and the frontend changes needed to support this functionality

* don't show slashes for now

frigate/api/defs/query/media_query_parameters.py

@@ -1,7 +1,8 @@
 from enum import Enum
-from typing import Optional
+from typing import Optional, Union
 
 from pydantic import BaseModel
+from pydantic.json_schema import SkipJsonSchema
 
 
 class Extension(str, Enum):
@@ -46,3 +47,10 @@ class MediaMjpegFeedQueryParams(BaseModel):
 class MediaRecordingsSummaryQueryParams(BaseModel):
     timezone: str = "utc"
     cameras: Optional[str] = "all"
+
+
+class MediaRecordingsAvailabilityQueryParams(BaseModel):
+    cameras: str = "all"
+    before: Union[float, SkipJsonSchema[None]] = None
+    after: Union[float, SkipJsonSchema[None]] = None
+    scale: int = 30