oidc: require custom username

oidc-gateway/deployment.yml

@@ -116,6 +116,8 @@ spec:
               value: '*'
             - name: PREFERRED_EMAIL_DOMAIN # try to make primary email consistent
               value: 'k-space.ee'
+            - name: REQUIRE_CUSTOM_USERNAME
+              value: 'true'
           envFrom:
             - secretRef:
                 name: redis-oidc-gateway-owner-secrets