Allow post to only federate within certain regions

[spaceottercode]

Pitch

Not sure if this is possible in ActivityPub but it would be nice if one (either the admin and/or user) could restrict where a post can & cannot federate between servers based on the server's region/country.

This is very similar to #27689 except that it is only concerned where the server is hosted and not the user.

Motivation

With the advent of threads it has become clear that people may be reluctant to join the fediverse due to the inability to recall a post they have authored. It may prove advantageous for admins (or maybe even users too) to have the ability to choose, from within Mastodon, which countries their posts freely federate to. This way, admins (and possibly users) could choose to narrow their federally diseminated content to countries with laws that respect & give users the right to remove content they have authored (or be "forgotten").

As to which countries? That will be up to the admin and or user, and maybe a list will be floated around. The default should ofc be all countries (or whatever it is now). Doing this on a user basis could possibly be trickier.

If it takes only one normal non-rogue server to defeat this system & there are no viable or adequate workarounds, then maybe disregard.

[nemobis]

How is this different from Limited federation mode? There are hundreds of jurisdictions out there, multiplied by thousands of laws which may or may not be applicable. As an instance admin worried about legal implications of federating with instances from a certain jurisdiction, you need to consult your lawyers to decide on criteria according to which you want to federate with an instance, or not, and then apply said criteria on a case by case basis.