[MM-25657] api4/config: add config migrate endpoint (#14928)

* api4/config: add config migrate endpoint

* api4/config: reflect review comments

* fix i18n lint error

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

i18n/en.json

@@ -1110,6 +1110,10 @@
     "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.config.migrate_config.app_error",
+    "translation": "Failed to migrate config store."
+  },
   {
     "id": "api.config.update_config.clear_siteurl.app_error",
     "translation": "Site URL cannot be cleared."