[Feature request] Ability to search within a playlist.

[pbsds]

I would love to be able to search within playlists.

My Favorites playlist has nearly 3k videos now, and YouTube, despite being owned by Google, is terrible at letting you search through collections. I've used youtube-dl + grep to do search my playlists until now, but that is incredibly unwieldy.

There might not be any suitable API endpoint, meaning the invidious instance would have to enumerate the whole playlist and perform the query server-side. Due to rate-limiting, it might be smart to gate this feature behind a setting.

[SamantazFox]

Related: #3959