Update license.go (handled error) (#28410)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/i18n/en.json

@@ -2224,6 +2224,10 @@
     "id": "api.license.add_license.array.app_error",
     "translation": "Empty array under 'license' in request."
   },
+  {
+    "id": "api.license.add_license.copy.app_error",
+    "translation": "Failed to copy license."
+  },
   {
     "id": "api.license.add_license.expired.app_error",
     "translation": "License is either expired or has not yet started."