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