owncloud/core

Enhancement: Add test receiver mail in Email Settings Admin Panel

With this change the admin needs to provide a test receiver mail address while
sending test mails in the Email Settings Admin Panel.
This has the advantage that the admin does not need to go back to user settings
and set the own mail address.
The user's own email will be set as preselected value if set.

https://github.com/owncloud/core/pull/39297
https://github.com/owncloud/core/issues/33018