fix(NewUserDialog): update group selection to prevent admin group from being assigned as subadmin

[Arsalanulhaq]

Summary

This pull request updates the group selection logic in the NewUserDialog.vue component to prevent users from being assigned as sub-admins of the admin group. The main change is the introduction of a new computed property from UserRow.vue to filter out the admin group from the selectable options for sub-admin assignment.

Group selection improvements:

• The :options prop for the sub-admin group selection now uses the new availableSubAdminGroups computed property, ensuring the admin group is excluded from the list of assignable sub-admin groups.
• Added the availableSubAdminGroups computed property, which filters out the admin group from availableGroups.

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

[CarlSchwan]

lint CI is failing but looks good.

And this does need the same code also in the backend, as we shouldn't rely only on client side verification ;)

[Arsalanulhaq]

lint CI is failing but looks good.

And this does need the same code also in the backend, as we shouldn't rely only on client side verification ;)

@CarlSchwan Thanks for your review.
The backend checks are already there apps/provisioning_api/lib/Controller/UsersController.php.
The lint issue is not coming from this NewUserDialog.vue file

[Antreesy]

/compile

[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

[Antreesy]

/backport c81422e to stable32

[Antreesy]

/backport c81422e to stable31