[feature] Implement exclusive lists

[VyrCossont]

Description

This pull request implements Hometown-style exclusive lists, compatibly with vanilla Mastodon's current API.

Fixes #2616

Checklist

• [x] I/we have read the GoToSocial contribution guidelines.
• [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• [x] I/we have not leveraged AI to create the proposed changes.
• [x] I/we have performed a self-review of added code.
• [x] I/we have written code that is legible and maintainable by others.
• [x] I/we have commented the added code, particularly in hard-to-understand areas.
• [x] I/we have made any necessary changes to documentation.
• [x] I/we have added tests that cover new code.
• [x] I/we have run tests and they pass locally with the changes.
• [x] I/we have run go fmt ./... and golangci-lint run.
• [x] I/we have tested this end to end in a prod environment with a Fedi client that supports exclusive lists

[VyrCossont]

Testing this end-to-end is a bit tricky: of the clients I tried today, Semaphore doesn't support lists at all, Elk doesn't support setting any list options other than the title, and Phanpy supports lists and the exclusive flag, but doesn't support setting the exclusive flag for GtS instances yet.

in Feditext, you can test exclusive lists by scrolling down to its advanced preferences and set "API compatibility mode" to "Enable all API calls, attempt error recovery", which disables most feature gating. (You'll want to turn that API compatibility mode off later, because Feditext will also call API endpoints that don't exist, which can trip wary WAFs like CrowdSec when they assume the site's being mapped for an attack.) Future Feditext builds will enable exclusive lists for whatever GtS version includes it.

[VyrCossont]

Confirmed that you can't follow yourself in GtS, and thus can't add yourself to a list (internally, this requires that a follow exists), so you can't add yourself to an exclusive list and thus prevent yourself from seeing your own posts in your home timeline.

[tsmethurst]

This looks great :) Nice simple PR that will be really useful. Just a couple comments from me. Once those are resolved we can squerge this!

[NyaaaWhatsUpDoc]

have left a handful of comments but other than that looks good :)