[Notifications] respect permission for recipients

[heigpa]

Steps to reproduce

• Login as admin
• Send a notification
• Open the recipients drop down

Actual behaviour

• all users are shown

Expected behaviour

• only users/groups with notification permission should be shown

Additional info. With the superuser, the recipient list is empty.

Environment

• Studio Nightly
• Windows
• Google Chrome

[Corepex]

Backend Ticket: pimcore/studio-backend-bundle#1136