[chore] Move local account settings to separate db table

[tsmethurst]

Description

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This pull request migrates account settings for local accounts to a separate table, and adds functionality for selecting + updating those settings.

The reasoning for this: we were storing more and more columns for accounts which would never be used except for local accounts, which widens the accounts table pointlessly. By moving settings for local accounts to another table, we can expand the amount of settings available to users without having to worry about mashing more unused settings into the main accounts table.

Migration tested with a local postgres and a local sqlite, seems OK on both.

Checklist

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• I/we have read the GoToSocial contribution guidelines.
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• 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.

[daenney]

This makes sense to me. With the exception of the storing the settings separately, the rest of the code is updating how settings are fetched etc. Changes to the tests make sense in light of that.