Don't try to auto-create special groups

[adorton-adobe]

Description
Want to avoid this error when targeting special groups with auto-create enabled.

CRITICAL processor - Unable to create %s user group: '_support_admin' on 'Sign' (error: '_support_admin': Illegal group name)

(this message also has a formatting issue)

Group create should check group name syntax, refuse to create special groups and log a warning that group creation was skipped.

Steps to reproduce

Testing/reproducing this issue requires an admin group that isn't returned in the org's group list from a UMAPI groups query. Otherwise the auto-create logic will not trigger.

The UMAPI will generally omit admin roles from the group list that have never had someone assigned to them.