Mark confidential settings as secrets

Author: hanzei

plugin.json

@@ -25,7 +25,8 @@
             "display_name": "Webhook Secret:",
             "type": "generated",
             "help_text": "The secret used to authenticate the webhook to Mattermost.",
-            "regenerate_help_text": "Regenerates the secret for the webhook URL endpoint. Regenerating the secret invalidates your existing Confluence integrations."
+            "regenerate_help_text": "Regenerates the secret for the webhook URL endpoint. Regenerating the secret invalidates your existing Confluence integrations.",
+            "secret": true
         }
     ]
   }