feat: Add announcements

[madkarmaa]

What's this?

This is a new, more updated continuation of #195

TODO:

• Show banner for latest unread announcement (feat: Add banner for when the API is down #254)

[Ushie]

Deleting tags does not behave like when creating a new announcement, they should disappear once unchecked

It has nothing to do with whether or not you're creating an announcement

Tags that already exist in the API will not disappear, tags that you've created in that draft will disappear once unchecked

[Ushie]

Unread latest announcement should be shown as a banner on the website.

The banners PR is not complete

[Ushie]

Nullability is not handled properly

ReVanced API seems to also not respect it

Creation:

Result:

[oSumAtrIX]

Deleting tags does not behave like when creating a new announcement, they should disappear once unchecked

It has nothing to do with whether or not you're creating an announcement

Tags that already exist in the API will not disappear, tags that you've created in that draft will disappear once unchecked

Even if they don't disappear in the API, they do for the announcement itself. So if you uncheck a tag, it should be removed. Adding it back via the same name, would not create a new tag because it already exists. This behaviour is the same as on YouTube if you tag videos.

Unread latest announcement should be shown as a banner on the website.

The banners PR is not complete

In that case it should be looked into so that this PR can rebase onto it.

ReVanced API seems to also not respect it

The tags and attachments fields are non nullable. However I'll change that. For author the issue still applies (and once the other fields are nullable, there too)