Quota requests

[marcoambrosini]

When someone isn't allowed to create a team-folder themselves, they can request one; an admin approves or adjusts the quota.

We need:

• Front-end flow in the circles app
• Admin flow in the teams settings

[jospoortvliet]

Ref nextcloud/groupfolders#4975

[alimmroth]

I think a group should be defined in the global team-settings, which gets the requests to approve them.
This could happen via notifications.

In addition in the teams app, members of this group should see a separate page in the left navigation bar, where they see a list of the pending requests. There they might also select multiple and batch-allow.