feat(shop-checkout): add plugin (#3337)

* feat(plugin): ShopCheckout

* Add typings for returned promises

src/@ionic-native/plugins/shop-checkout/index.ts

@@ -0,0 +1,80 @@
+import { Injectable } from '@angular/core';
+import { Plugin, Cordova, IonicNativePlugin } from '@ionic-native/core';
+
+/**
+ * @name ShopCheckout
+ * @description
+ * This is a plugin that allows your Ionic app to use ShopChecout for Android.
+ * Follow the offical documentation to setup this plugin correctly: https://developer.shoptopup.com/docs/shoptopup-for-cordovaphonegap
+ *
+ * @usage
+ * ```typescript
+ * import { ShopCheckout } from '@ionic-native/shop-checkout/ngx';
+ *
+ *
+ * constructor(private shopCheckout: ShopCheckout) { }
+ *
+ * ...
+ *
+ * this.shopCheckout.registerAgent();
+ * ...
+ * this.shopCheckout.openProducts();
+ *
+ * ```
+ */
+@Plugin({
+  pluginName: 'ShopCheckout',
+  plugin: 'cordova-plugin-shop-checkout',
+  pluginRef: 'shopCheckout',
+  repo: 'https://github.com/tradedepot/cordova-shop-checkout',
+  platforms: ['Android']
+})
+@Injectable()
+export class ShopCheckout extends IonicNativePlugin {
+  /**
+   * Register an agent
+   * @param options {any} Options
+   * @return {Promise<void>} Returns a promise
+   */
+  @Cordova()
+  registerAgent(options: any): Promise<void> {
+    return;
+  }
+
+  /**
+   * Open products view
+   * @param options {any} Options
+   * @return {Promise<void>} Returns a promise
+   */
+  @Cordova()
+  openProducts(options: any): Promise<void> {
+    return;
+  }
+
+  /**
+   * Open trannsactions view
+   * @param options {any} Options
+   * @return {Promise<void>} Returns a promise
+   */
+  @Cordova()
+  openTransactions(options: any): Promise<void> {
+    return;
+  }
+
+
+  /**
+   * @return {Promise<void>} Returns a promise
+   */
+  @Cordova()
+  logout(options: any): Promise<void> {
+    return;
+  }
+
+  /**
+   * @return {Promise<boolean>} Returns a promise
+   */
+  @Cordova()
+  isInitialized(): Promise<boolean> {
+    return;
+  }
+}