Replaced query for SAML users and service accounts

In the group and project member pages, the invite user modal is used to
query and filter users. When the top-level group has a SAML provider
enabled and the option `Enforce SSO-only authentication for web activity
for this group` only SAML users are returned.

Following https://gitlab.com/gitlab-org/gitlab/-/merge_requests/134570,
we replace the user API endpoint (`/api/v4/users.json`) for the new
group user API endpoint (`/api/v4/groups/[groupId]/users.json`) to get a
list users that have a SAML identity connected to the group, or service
accounts created by the group or subgroups

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/424505