feature: user configuration of email preferences

[isXander]

All of this is already set up in the backend, but the frontend was not hooked up at all.

• Adds new "Email notifications" tab to settings
  • Only shows if the user has an email set
  • Filters to only the user-configurable notification types as-defined by the database
• Adds some internal API routes to allow the frontend to configure
• Adds new upsert method to email notification item

[isXander]

Currently looks like this

Could make it like this?

Labrinth has some setup to support future notification channels in the future. But currently it would just be email

[Prospector]

I think checkboxes would likely be better, and each row likely doesn't need a description when most of them are just the title restated in a sentence anyway, to make it less cramped

[IMB11]

Users shouldn't be allowed to turn off any of these emails as they're critical - I think this is why we haven't implemented this yet because there aren't any "promotional"/optional emails yet. (Apart from project updates)

[isXander]

The backend already defines which notification types are not user configurable, and only sends the frontend a list of user configurable ones. If there are some that need to be adjusted, that's a simple database tweak.

https://github.com/modrinth/code/pull/5426/changes#diff-35b5820591a58601dfe3dad728bb613a1eacb76ae6f510367805447d7d090340R54