[feature] Create/update/remove domain permission subscriptions

[tsmethurst]

Description

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

This PR adds database functions and frontend + api bits for creating, viewing, updating, and removing domain permission subscriptions. Currently the domain permission subscriptions aren't actually activated, this is to come in the next PR.

Documentation + tests and all that jazz to follow, also in a separate PR, to keep things manageable.

Checklist

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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 not leveraged AI to create the proposed changes.
• 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.

[NyaaaWhatsUpDoc]

given we return error on an empty string here, is it worth just making this field type a non-ptr?

[NyaaaWhatsUpDoc]

same as above

[NyaaaWhatsUpDoc]

same as below