Add unique users creating sessions with LDAP/SAML/OAuth2 to usage ping (Access GMAU)

Problem

In gitlab-org/manage/general-discussion#17232, we described the need for a Group MAU for Access. This should be a measure of the number of unique users taking an action that is important to the goals of the Access group.

Proposal

• Add the number of users creating sessions using "enhanced authentication". We can constrain this definition to LDAP/SAML/OAuth/Smartcard.
• We should track these as separate counts as well as an aggregated, deduplicated total across all methods (the number of unique users logging in with LDAP or SAML or OAuth or Smartcard).

This should cover all tiers of functionality:

• Self-managed and GitLab.com
• Free and paid features (e.g. self-managed SAML and SAML SSO for Groups)