Make LDAP be able to skip local 2FA (#16954)

This PR extends #16594 to allow LDAP to be able to be set to skip local 2FA too. The technique used here would be extensible to PAM and SMTP sources.

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/auth/source/oauth2/source_authenticate.go

@@ -13,3 +13,6 @@ import (
 func (source *Source) Authenticate(user *models.User, login, password string) (*models.User, error) {
 	return db.Authenticate(user, login, password)
 }
+
+// NB: Oauth2 does not implement LocalTwoFASkipper for password authentication
+// as its password authentication drops to db authentication