Mention groups or everyone in the comments section (@all @group)

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Feature request

Which Nextcloud Version are you currently using: (see administration page)
31.0.10

Is your feature request related to a problem? Please describe.
No, just a way to deal with various use cases.

Describe the solution you'd like
Use the mention @ feature for groups of users as registered in the "Accounts" administrative settings or for all users

Describe alternatives you've considered
none.

Additional context
Let's say I have announced a maintenance which was not successful and have to reschedule. Or let's say I'd like to drop a reminder about an announcement. Sometimes is better to write it as a comment mentioning all or specific groups of users than creating another announcement.

No files, tests, or entry points are identified in the issue. Start by locating the existing comment-mention implementation and the Accounts group model, then determine the notification and permission requirements for mentioning groups or all users. Done means an agreed scope and tested behavior for both mention forms.