[Feature request] A way to categorize subscriptions

[gptlang]

Is your feature request related to a problem? Please describe.

I have 254 subscriptions, some less important than others. Shorts #2585 and other content regularly clutters the feed such that I miss important ones.

Describe the solution you'd like

A dropdown can be added to the subscribe button which allows the subscription can be added to pre-defined lists. Similar to the Playlists section, we can have "Sublists" where these lists are stored.

Describe alternatives you've considered

Write my own UI for that via the invidious APIs. It might be inefficient to fetch /api/v1/channels/:CHANNEL_ID repeatedly for every channel & caching it so I suppose another feature request would be to expose whatever invidious uses to keep track of subscriptions such that I can send an array of channel IDs and receive a small paginated response.