feat(emm-app-config): add plugin (#3181)

* Add Emm App Config plugin

Add [emm-app-config](https://github.com/oracle/cordova-plugin-emm-app-config) plugin to retrieve EMM application configuration

* Update index.ts

src/@ionic-native/plugins/emm-app-config/index.ts

@@ -0,0 +1,61 @@
+import { Injectable } from '@angular/core';
+import { Cordova, IonicNativePlugin, Plugin } from '@ionic-native/core';
+import { Observable } from 'rxjs';
+
+/**
+ * @name Emm App Config
+ * @description
+ * This plugin provides information on EMM application configuration
+ *
+ * Requires the Cordova plugin: `cordova-plugin-emm-app-config`. For more info, please see the [Cordova EMM App Config Plugin Docs](https://github.com/oracle/cordova-plugin-emm-app-config).
+ *
+ *
+ * @usage
+ * ```typescript
+ * import { EmmAppConfig } from '@ionic-native/emm-app-config/ngx';
+ *
+ *
+ * constructor(private readonly emmAppConfig: EmmAppConfig) { }
+ *
+ * ...
+ *
+ * // Get all the values of the emm app configuration
+ * const values = this.emmAppConfig.getValue();
+ *
+ * // Get specific value of the emm app configuration
+ * const value = this.emmAppConfig.getValue('serverUrl');
+ *
+ * // Get an event every time the emm app config changes
+ * this.emmAppConfig.registerChangedListener()
+ *   .subscribe(() => console.log('App config changes'));
+ *
+ * ```
+ */
+@Plugin({
+  platforms: ['Android', 'iOS'],
+  plugin: 'cordova-plugin-emm-app-config',
+  pluginName: 'EmmAppConfig',
+  pluginRef: 'cordova.plugins.EmmAppConfig',
+  repo: 'https://github.com/oracle/cordova-plugin-emm-app-config',
+})
+@Injectable()
+export class EmmAppConfig extends IonicNativePlugin {
+
+  /**
+   * Get value from the Emm application configuration.
+   * @param configKey {string}  Key of the value to get, or null to get all the values as an object.
+   * @return {any} Returns configuration on an object
+   */
+  @Cordova({ sync: true }) getValue(configKey?: string): any {
+    return;
+  }
+
+  /**
+   * Register a listener that will be invoked when the application configuration is changed.
+   * @return {void}
+   */
+  @Cordova({ observable: true }) registerChangedListener(): Observable<void> {
+    return;
+  }
+
+}