Add management UI for featured tags and profiles, within web app

[trwnh]

GET /api/v1/endorsements exists as an API but is unmanageable in the Mastodon frontend, as best as I can tell. You can only feature or unfeature a profile (if you know who you have already featured), but that's about it. A menu entry below "pinned toots" would probably be best.

Likewise, the new "featured tags" API is also unmanageable in the frontend -- but unlike featured profiles, it is at least manageable in the settings under Settings > Profile > Featured hashtags.

Somewhat related: #8162 is a subset. #9646 is for actually displaying featured accounts in the web app (and not just the public profile page). There could be a similar issue for displaying featured tags, but I haven't found one. Closest thing is #7988 which is for following only a tagged subset of posts from a profile.