Indicate to admins that users that are the sole owner of a group can only be hard deleted

Follow up from #337156 (closed)

In #332846 (closed) we moved all the admin user actions from cards to a dropdown. Before we did this there was a message that no longer exists:

Now there is no message explaining to admins why Delete user and contributions (hard delete) exists but Delete user does not exist.

Proposal

✏ Figma work file

Dropdown	Dropdown in users list	Modal pop up on delete	Groups and projects container in user details

Implementation plan

1. Remove if @user.can_be_removed? from app/helpers/admin/user_actions_helper.rb#L53
2. Add expose :solo_owned_groups to app/serializers/admin/user_entity.rb#L14
3. Add soloOwnedGroups: 'SOLO_OWNED_GROUPS' to app/assets/javascripts/vue_shared/components/user_deletion_obstacles/constants.js#L4
4. Update app/assets/javascripts/vue_shared/components/user_deletion_obstacles/user_deletion_obstacles_list.vue to render the correct message.
   • Create new obstacle components and then dynamically render the correct obstacle component.
5. Update specs

Availability & Testing

Ensure end-to-end tests pass by running the package-and-qa job