feat: WA Business Labels support (#407)

* Get all labels
* Get chats by label
* Get labels assigned to chats

Co-authored-by: Pedro S. Lopez <pslamoros@hotmail.com>
Co-authored-by: Pedro Lopez <pedroslopez@me.com>

src/structures/Label.js

@@ -0,0 +1,50 @@
+'use strict';
+
+const Base = require('./Base');
+// eslint-disable-next-line no-unused-vars
+const Chat = require('./Chat');
+
+/**
+ * WhatsApp Business Label information
+ */
+class Label extends Base {
+    /**
+     * @param {Base} client
+     * @param {object} labelData
+     */
+    constructor(client, labelData){
+        super(client);
+
+        if(labelData) this._patch(labelData);
+    }
+
+    _patch(labelData){
+        /**
+         * Label ID
+         * @type {string}
+         */
+        this.id = labelData.id;
+
+        /**
+         * Label name
+         * @type {string}
+         */
+        this.name = labelData.name;
+
+        /**
+         * Label hex color
+         * @type {string}
+         */
+        this.hexColor = labelData.hexColor;
+    }
+    /**
+     * Get all chats that have been assigned this Label
+     * @returns {Promise<Array<Chat>>>}
+     */
+    async getChats(){
+        return this.client.getChatsByLabelId(this.id);
+    }
+
+}
+
+module.exports = Label;