Add Video Metadata to Summary

[finnless]

Possible approaches:

1. Change video loader to a custom loader class that inherits from langchain's YoutubeLoader
   https://github.com/hwchase17/langchain/blob/560c4dfc98287da1bc0cfc1caebbe86d1e66a94d/langchain/document_loaders/youtube.py#L142-L250
   YoutubeLoader creates a document from transcript instead of transcript_pieces.
2. Or I could just call YoutubeLoader._get_video_info(self) where self only needs a self.video_id

Additional metadata would give the model additional context about the video.