Streaming media item creation during indexing

[kieraneglin]

What's new?

• Adds behaviour to indexing that listens to the file yt-dlp writes to and creates MediaItem records as they come in
  • This HUGELY improves the indexing process since it used to run indexing -> creation -> downloading in serial
• Adds behaviour to the above to enqueue download of media items post-index
• Adds FileSystemUtils module with generate_metadata_tmpfile method to generate a blank tmpfile of a given type
• Adds a FileFollowerServer method for listening to file changes and performing actions on just the changes
• Adds Media.pending_download? to determine if an individual MediaItem should be downloaded

What's changed?

• Updates command runner to optionally take a filepath of the file it'll write its output to
• Removes command_opts arg from VideoCollection.get_media_attributes since it was unused
• Renames index_media_items in SourceTasks to index_and_enqueue_download_for_media_items to better reflect its purpose
• Updates index_and_enqueue_download_for_media_items to now kickoff downloads for pending media itself without needing to call enqueue_pending_media_tasks specifically

What's fixed?

N/A

Any other comments?

N/A