Support per user per instance authentication

For anyone looking at this, note that I write this issue assuming the completion of https://www.drupal.org/project/social_post_mastodon/issues/3532697 📌 Update for Drupal 11 and Social Post 3.x compatibility Active

That issue fork is essentially being used to update the module architecture to later versions of social post, make it compatible with D11 (per the issue name), but also just to get the module working at all.

I don't have any plans to actually fulfill this issue request, and may actually shift toward the Social Post X module pattern, where the site actually only supports a single user, so that I don't have to worry about authenticating against Mastodon per Drupal user or worrying about supporting integration with multiple Mastodon api apps. I mostly wrote this for documentation purposes. Though if anyone comes across this and feels strongly one way or the other, do share your use case, and please help out if you are able.

The above mentioned issue fork is merged. On another note, I was considering the updated form element, and thinking it would be possible to serialize and store instance, client id, client secret as additional data. It is noteworthy that the addUserRecord function takes 'additional data' as an argument, which is currently unused.

Okay I'm a little bit more generous to this feature at the moment, and felt compelled to make it possible for some reason, despite not really needing it. The issue fork is working. I haven't yet removed the admin settings form, even though none of the module settings do anything now. This is because I actually do intend to add new settings to the module. I will probably just leave it and make a separate issue for adding new settings.

Before wrapping this up, I want to consider whether I would like to structure the instance data a little bit. I'm not even storing it in an associative array right now, but it would be smart to anticipate that I will probably want to store more information in the additional data field at some point.

Also, I need to set the instance in the Rules Toot class. After that, I think this should be good.