Merge branch 'harishsr-docs-saml-group-sync-multiple' into 'master'

Document that SAML Group Sync only works with one provider

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/107686



Merged-by: Jon Glassman <jglassman@gitlab.com>
Approved-by: Jon Glassman <jglassman@gitlab.com>
Co-authored-by: Harish Ramachandran <harish@gitlab.com>