added the custom icon and username for the outgoing webhook and its response (#9141)

* 8272 added the username and icon as part of the model and persisted the same

* 8272 added the custome icon and name when set to the web hook response

* 8272 changed the infinte loop to timeout after 5 seconds

* 8272  fixed review comments

i18n/en.json

@@ -4454,6 +4454,13 @@
     "id": "model.outgoing_hook.is_valid.words.app_error",
     "translation": "Invalid trigger words"
   },
+  {
+    "id": "model.outgoing_hook.username.app_error",
+    "translation": "Invalid username"
+  },{
+    "id": "model.outgoing_hook.icon_url.app_error",
+    "translation": "Invalid icon"
+  },
   {
     "id": "model.plugin_command.error.app_error",
     "translation": "An error occurred while trying to execute this command."