feat(Message): add support for crossposting (#4105)

Co-authored-by: Advaith <advaithj1@gmail.com>
Co-authored-by: Joe <56809242+Jo3-L@users.noreply.github.com>
Co-authored-by: Jan <66554238+Vaporox@users.noreply.github.com>
Co-authored-by: Noel <icrawltogo@gmail.com>

src/structures/Message.js

@@ -448,6 +448,22 @@ class Message extends Base {
     });
   }
 
+  /**
+   * Publishes a message in an announcement channel to all channels following it.
+   * @returns {Promise<Message>}
+   * @example
+   * // Crosspost a message
+   * if (message.channel.type === 'news') {
+   *   message.crosspost()
+   *     .then(() => console.log('Crossposted message'))
+   *     .catch(console.error);
+   * }
+   */
+  async crosspost() {
+    await this.client.api.channels(this.channel.id).messages(this.id).crosspost.post();
+    return this;
+  }
+
   /**
    * Pins this message to the channel's pinned messages.
    * @param {Object} [options] Options for pinning