feat(Webhook): add type property and created* getters (#3585)

* feat(Webhook): add created* getters

* feat(Webhook): add type property

* typings(WebhookFields): use primitive string for url getter

Co-Authored-By: Gryffon Bellish <owenbellish@gmail.com>

* fix(Webhook): token can be null

Co-authored-by: Gryffon Bellish <owenbellish@gmail.com>

src/util/Constants.js

@@ -628,6 +628,19 @@ exports.MembershipStates = [
   'ACCEPTED',
 ];
 
+/**
+ * The value set for a webhook's type:
+ * * Incoming
+ * * Channel Follower
+ * @typedef {string} WebhookTypes
+ */
+exports.WebhookTypes = [
+  // They start at 1
+  null,
+  'Incoming',
+  'Channel Follower',
+];
+
 function keyMirror(arr) {
   let tmp = Object.create(null);
   for (const value of arr) tmp[value] = value;