[feature] Store admin actions in the db, prevent conflicting actions

[tsmethurst]

Description

If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.

If this is a documentation change, please briefly describe what you've changed and why.

This pull request updates our handing of admin actions (domain block, domain unblock, account suspend, etc) in the following ways:

When an admin action is performed on a domain or an account, store a record of that action in the database.

Previously, we only stored admin account actions.

Now, we can also store domain block / unblock actions (for starters), as well as completion time of said actions, and any errors that occurred while the action was being processed. In future this could be used to allow admins to review a timeline of actions. This is, imo, pretty sick 😎

Don't allow multiple actions that target the same resource to run at the same time.

This is achieved by storing running admin actions in a map keyed by [TargetCategory]/[TargetID], and removing them from the map when they're finished.

For example, a domain block for the domain example.org would have the key domain/example.org. A domain allow for the domain example.org would ALSO have the key domain/example.org. Same goes for another domain block for that domain. This ensures that these two actions cannot run at the same time. Now, an API request to perform a second action on an existing key will just get a 409 error back that looks something like:

AccountAction: an action (account/01H90S1CXQ97J9625C5YBXZWGT) is currently running (duration 25.566746ms) which conflicts with the attempted action: wait until this action is complete and try again

Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: [ ] -> [x]

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[tsmethurst]

Think this should be ready to go!

[NyaaaWhatsUpDoc]

nice work comrade 🤠 very nice looking PR 👩‍🍳 👌