[OpenCast] Add extractors (#1905)

Original PR: https://github.com/ytdl-org/youtube-dl/pull/26934
Authored by: bwildenhain, C0D3D3V

yt_dlp/extractor/extractors.py

@@ -1040,6 +1040,10 @@ from .ooyala import (
     OoyalaIE,
     OoyalaExternalIE,
 )
+from .opencast import (
+    OpencastIE,
+    OpencastPlaylistIE,
+)
 from .openrec import (
     OpenRecIE,
     OpenRecCaptureIE,