Extract Youtube Subscriptions for Pages

[NWuensche]

In this PR, I added a way to get the subscription count for pages. Right now, "sometimes" when I open a youtube channel, it's type is "Page" and therefore no subscription count is displayed. However, one can extrat the subscription count from the metaData for pages.

With "sometimes", I mean that there seems to be a 25% change that when I open a youtube channel in the app, it's type is page. I haven't found any understandable ways on when this happens, it seems random to me. It can even happen that a channel that is not a page becomes a page when I restart the app.

• [x] I carefully read the contribution guidelines and agree to them.
• [x] I have tested the API against NewPipe.
• [x] I agree to create a pull request for NewPipe as soon as possible to make it compatible with the changed API.

[AudricV]

Thanks, but this should be already fixed by #1170, in a more dynamic and safer way than yours. Closing you pull request due to this reason.