Optional turn server support

CloudronManifest.json

@@ -15,7 +15,7 @@
     "ldap": {},
     "postgresql": {},
     "sendmail": { "supportsDisplayName": true },
-    "turn": {}
+    "turn": { "optional": true }
   },
   "manifestVersion": 2,
   "website": "https://matrix.org",
@@ -30,7 +30,7 @@
     "https://screenshots.cloudron.io/org.matrix.synapse/3.png"
   ],
   "postInstallMessage": "file://POSTINSTALL.md",
-  "minBoxVersion": "7.2.0",
+  "minBoxVersion": "7.3.1",
   "forumUrl": "https://forum.cloudron.io/category/50/matrix-synapse-riot",
   "documentationUrl": "https://docs.cloudron.io/apps/synapse/",
   "optionalSso": true