Tags for user and group objects

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Is your feature request related to a problem? Please describe.
I have a lot of user in nextcloud. I need to isolate users inside their groups to prevent them from seeing other users (users from one group should not see users from another group). In the same time I need to manage access to applications (f.e. richdocuments or talk). In app config I can provide list of groups who will have access to app. but there can be a lot of groups. Each time I add new group, I need to reconfigure application too.

Describe the solution you'd like
In this case I would like to use tags for users/groups. Once setup tag, configure application (provide access to users/groups who have tag) and don't care about reconfiguration.
In application config also add possibility to configure access by tag.
Also add API endpoint to setup tag for user/group.

Start by reviewing the existing user and group visibility controls, application access configuration, and user/group API entry points. Define how tags would be assigned, exposed through the API, and consumed by applications before implementing anything. Done means users can be isolated by group and application access can be configured by tags without per-group reconfiguration.