ServiceAccounts: enable service accounts after IsRealUser change (#58263)

* suppor service accounts

* add: IsServiceAccount to scheduleUser in scheduler

Co-authored-by: eleijonmarck <eric.leijonmarck@gmail.com>

pkg/services/user/model.go

@@ -306,6 +306,9 @@ func (u *SignedInUser) GetCacheKey() (string, error) {
 	if u.IsApiKeyUser() {
 		return fmt.Sprintf("%d-apikey-%d", u.OrgID, u.ApiKeyID), nil
 	}
+	if u.IsServiceAccountUser() { // not considered a real user
+		return fmt.Sprintf("%d-service-%d", u.OrgID, u.UserID), nil
+	}
 	return "", ErrNoUniqueID
 }