Comments: Add support for new format

[ChunkyProgrammer]

Closes #4566

This should fix the issues with most comments but there are still some more changes that would need to be made like adding support for formatting (bold, italic, underline) and channel emojis. The new format for these changes is similar to how descriptions of commandRuns.

[Yetangitu]

See #4566 (comment), testing a number of video's with this PR applied shows comments loaded on every load. Given that this PR does not remove the original comment code but uses it as a fallback if the 'new' comment model is not present this seems to be a workable solution. Once YT finishes its A/B testing and settles on one of the current comment models the fallback (or the new code if they decide to ditch the new model) can be removed.

[Yetangitu]

For those who can not (or do not want to) build a release themselves and who feel confident (or silly) enough to trust a random binary put on the 'net I put a release on my fork:

https://github.com/Yetangitu/invidious/releases/tag/0.20.1-PR4576

Here's the actual binary, built on Debian stable:

https://github.com/Yetangitu/invidious/releases/download/0.20.1-PR4576/invidious

This is what I'm running on my server, if it works for me it might work for you.

[SamantazFox]

Outside my comments below, everything works nicely, both on video comments as well as community post comments! Thanks for the PR :)

[SamantazFox]

I'll definitely need to work on decoupling the upstream from the downstream JSON logic one day. This is becoming quite a problem. Also I realized that the community posts use a different chunk of logic, where all of that could be unified.

[TheFrenchGhosty]

I've been using it for more than a day now via the test instance, seems to work perfectly (seems also faster and more reliable (?) that the previous implementation.

[unixfox]

have been running fine on yewtu.be for 2 days: https://github.com/yewtudotbe/invidious-custom/blob/master/patches/012-4576.patch