Create a system user that can be leveraged

During the development of the activity chooser redesign we opted to use the guest user to assign recommended activities, after the release it turned out that a few Moodle sites are lacking guest users either due to accidental or intentional removal.

This highlighted to our team that there is a need to have a system user that we can guarantee is there and can not be deleted or removed, This would be of use as currently we have either:

1. Guest user
   1. Could be removed due to a GDPR bug which has since been resolved
   2. More focused towards allowing guests into the site before registering / logging in
2. Primary admin
   1. Which can be reassigned and then removed
   2. System / subsystem items shouldn't in my mind be assigned to a modifiable user
   3. Moving away from this would assist developers in avoiding weird side effects in their plugins if they assign items to this role and then don't manage their data when the primary admin is changed

Neither of these users are really system users that both Moodle HQ & 3rd party developers can readily depend on for the reasons mentioned above and most likely more.

If this issue were to go ahead then in my mind the example usage to assist with integration would be the migration of the recommended activities to the new user.

Thoughts and proposals welcome.

Cheers,