Merge branch 'feat/member-guideline' into 'master'

Add member guideline to admin appearance settings

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/137942



Merged-by: Michał Zając <mzajac@gitlab.com>
Approved-by: Alex Pennells <apennells@gitlab.com>
Approved-by: Amelia Bauerly <abauerly@gitlab.com>
Approved-by: Michał Zając <mzajac@gitlab.com>
Reviewed-by: Roger Meier <r.meier@siemens.com>
Reviewed-by: Michał Zając <mzajac@gitlab.com>
Reviewed-by: charlie ablett <cablett@gitlab.com>
Reviewed-by: Lorena Ciutacu <lciutacu@gitlab.com>
Reviewed-by: Alex Pennells <apennells@gitlab.com>
Co-authored-by: Roger Meier <r.meier@siemens.com>