Add new SAML Group Sync topic to global navigation

With gitlab!89175 (merged) merged, we can now add it to the global navigation.

• Before: https://docs.gitlab.com/ee/user/group/saml_sso/group_sync.html
• After: http://eread-add-group-sync-nav-item.35.193.151.162.nip.io/ee/user/group/saml_sso/group_sync.html

CC @dblessing