fix(provisioning): Do not provision mail account for users without access to mail app

[DerDreschner]

When using the provisioning functionality, only the configured pattern where checked before pushing the mail account configuration into the database. This is fine as long as all users can use the mail app. But as the access to specific apps can be limited to specific groups, this can lead to accounts that are configured and synced in the background, yet being never used and only eat up precious resources.

To ensure this does not happen anymore, I use the IAppManager to check if the specific user has the right to use the mail app. If not, the provisioning for the user will be stopped.

This fixes #12057.

[DerDreschner]

@ChristophWurst : Should I add a migration to remove mail accounts from users that have no access to the mail app...? Or is that already being handled by a background job, etc.?