[Feature] Set default user settings as admin

[bo0tzz]

I have searched the existing feature requests to make sure this is not a duplicate request.

• Yes

The feature

As an admin, it would be nice to be able to decide on the default user settings for things like feature flags, locale, or notifications.

Platform

• Server
• Web
• Mobile

[JonahKr]

This is especially useful when supporting Mail Notifications.
While collecting images from multiple people in a shared album, by default everyone will get spammed with Mails.