[MM-31404] api4/config: return error when patching PluginSettings.EnableUploads (#16611)

* api4/config: return error when patching PluginSettings.EnableUploads

* reflect review comments

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

i18n/en.json

@@ -1142,6 +1142,10 @@
     "id": "api.config.update_config.clear_siteurl.app_error",
     "translation": "Site URL cannot be cleared."
   },
+  {
+    "id": "api.config.update_config.not_allowed_security.app_error",
+    "translation": "Changing {{.Name}} is not allowed due to security reasons."
+  },
   {
     "id": "api.config.update_config.restricted_merge.app_error",
     "translation": "Failed to merge given config."