[Enhancement] Include author thumbnails and number of subscribers in /subscriptions API

[blacklight]

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

I'm working on pulling Invidious subscriptions and playlists into my UI, and I'd like to render more information about the channels in the list.

Namely, currently the results only include entries in the following format:

{"author": "xkcd's What If?", "authorId": "UC6IxnFzHofFJ5X2PycSMsww"}

Describe the solution you'd like

A consistent response format on all the endpoints that return channels (probably this also means including authorThumbnails on video results).

I wouldn't go as far as including the full list of videos (there are dedicated endpoints for those already), but at least the metadata that is provided on /api/v1/channels/:id should be the same one also provided on /api/v1/auth/[notifications|subscriptions].

This is similar to what the Piped API already does. The fact that this metadata isn't provided on the Invidious API instead means that my UI won't show channel images or list of subscribers in the feed tab, nor in playlist views.

Describe alternatives you've considered

The obvious workaround would be to run a bunch of workers to fetch /api/v1/channels/:id whenever the user accesses the feed/playlist view in my UI, and maybe add some caching on top. But it would be obviously slow, harder to maintain, and the caching logic can easily be error-prone without the backend informing me whether a channel's metadata has changed.

Additional context

N/A

[absidue]

Invidious provides different information on different endpoints, because YouTube does. To be able to provide the extra information Invidious would have to make a lot more API requests, the requests that you said you don't want to do, which will just result in Invidious instances having even more problems with YouTube blocking them than they already do.