Merge branch '439623-strip-username-special-chars-on-ldap-signup' into 'master'

Additional cleanup for external usernames on oAuth and LDAP sign up

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145038



Merged-by: Bogdan Denkovych <bdenkovych@gitlab.com>
Approved-by: Bogdan Denkovych <bdenkovych@gitlab.com>
Reviewed-by: Andrew Evans <aevans@gitlab.com>
Co-authored-by: agius <andrew@atevans.com>