Add support for restrictive follow / honor answer to a follow request

[BentiGorlich]

At the moment we just expect that a "Follow" activity is replied to with a "Accept" activity. That is not always the case. Add support for that by adding a "accepted" column in the SQL table.

Of course all the delivery code has to account for that and filter out subscriptions that are not yet accepted

This is applicable for user <-> user, and user <-> magazine (and in the future even magazine <-> magazine) follows

[BentiGorlich]

So it is kinda implemented, but in a weird way. There is a separate table for follow requests and that table only gets filled when a user has set their profile to manually approve followers.
Imo there should not be a separate table, because whether a user manually approves their followers or not, servers always have to send Accept|Reject activities as an answer to a follower. So this should just be an int field or two bool fields in the follow table. As long as the request is neither accepted nor rejected we should display a "pending" on the profile. Additionally we should display something to let the user know whether another user is manually approving followers. Mastodon does it by displaying a 🔒 next to the display name of the user