WPB-19234: Allow team admins to bulk add users to user groups

[blackheaven]

https://wearezeta.atlassian.net/browse/WPB-19234

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[blackheaven]

The usual failing test:

[wire-server-enterprise@dynamic-backend-1.test-dk5d8go6lt1u.svc.cluster.local:Auth.testTooManyCookies] {"level":"Info","msgs":["Listening on 127.0.0.1:10079"]}

[blackheaven]

TODO

This is trivial, but I think it would be nice to test that non-team members and non-admins cannot add users to a user group, as well as the correct notifications are sent to users and admins.

[blackheaven]

@battermann can you have another look please? I have added test for edge cases and notifications.

[blackheaven]

Needs #4734 to be merged first

[battermann]

LGTM