feat(YouTube Music): add support version 6.20.51

[kitadai31]

Add support version 6.20.51.
This is the latest version that supports Android 5.0 - 6.0.

Integrations: inotia00/revanced-integrations#57

Not a big change.
I have tested all features, and fixed some found issues.

I'm also preparing to make ReVanced Manager compatible with Android 5.0.
(Not about my fork manager, as it is stuck on patcher v14...)

Note: If I you apply "Player components" patch to this version, the app will crash once on first launch.
However, this also occurs with the supported version v6.29.58 as well. (I haven't tried other versions.)
Therefore, this is not an issue of this PR.
I've already identified the cause of the crash, so I'll open a follow up issue later.

If you don't want to support 6.20.51, please close PR.

But before you do that, please reconsider.
I can collaborate with you.
For example, if a bug report for 6.20.51 is submitted, assign me and I'll try to fix the issue.
Also, when you add new features, you don't necessarily need to support 6.20.51. If the new feature brakes 6.20.51 unintentionally, I can try to fix.

[inotia00]

thanks