Implement client config/license endpoints for APIv4 (#5867)

i18n/en.json

@@ -47,6 +47,14 @@
     "id": "September",
     "translation": "September"
   },
+  {
+    "id": "api.config.client.old_format.app_error",
+    "translation": "New format for the client configuration is not supported yet. Please specify format=old in the query string."
+  },
+  {
+    "id": "api.license.client.old_format.app_error",
+    "translation": "New format for the client license is not supported yet. Please specify format=old in the query string."
+  },
   {
     "id": "api.admin.add_certificate.no_file.app_error",
     "translation": "No file under 'certificate' in request"