FEP-3b86: Activity Intents

### Describe the problem to be solved

[FEP-3b86: Activity Intents](https://codeberg.org/fediverse/fep/src/branch/main/fep/3b86/fep-3b86.md) make it possible for a remote server to display (for example) "Share" or "Like" buttons that lets PeerTube users interact with the remote pages using their home PeerTube account.

This is an easy addition that helps connect the social web together, in more ways than just through their timeline.

### Describe the solution you would like

[FEP-3b86: Activity Intents](https://codeberg.org/fediverse/fep/src/branch/main/fep/3b86/fep-3b86.md) is a small change to the data published by WebFinger that would improve how PeerTube connects to other Fediverse servers.

It is similar to the old oStatus "remote follows" but it is 1) works for any kind of Activity, not just `Follow`, and 2) has actual documentation. Implementing this FEP is as simple updating WebFinger results to include the URLs that let website visitors perform Activities on their own server (such as `Follow`, `Like`, or `Announce`). Then, other websites can use this information to display interactive buttons to take those actions.

I am not a Node developer, so I probably shouldn't try to make this change to PeerTube myself, but I'm happy to work with anyone who's interested in making this enhancement.

Read the linked FEP-3b86 specification first, then locate the code that builds PeerTube's WebFinger results. Check how ActivityPub actions such as Follow, Like, and Announce are represented there; done means the WebFinger response exposes the corresponding activity-intent URLs for remote websites.

Written by the indexing model from the issue text.