Added isOfficial

public/v2/apps/mailtrain.json

@@ -3,6 +3,7 @@
     "documentation": "Taken from https://github.com/Mailtrain-org/mailtrain/blob/development/docker-compose.yml",
     "displayName": "Mailtrain V2(Beta)",
     "description": "Mailtrain is a self hosted newsletter application built on Node.js (v10+) and MySQL (v8+) or MariaDB (v10+).",
+    "isOfficial": true,
     "dockerCompose": {
         "version": "3.8",
         "services": {