feat(branch-io): add initSessionWithCallback method (#3660)

Author: MaximBelov

src/@ionic-native/plugins/branch-io/index.ts

@@ -1,5 +1,6 @@
 import { Injectable } from '@angular/core';
 import { Cordova, IonicNativePlugin, Plugin } from '@ionic-native/core';
+import { Observable } from 'rxjs';
 
 export interface BranchIoPromise {
   $identity_id?: number;
@@ -105,6 +106,15 @@ export class BranchIo extends IonicNativePlugin {
     return;
   }
 
+  /**
+   * Initializes Branch with callback
+   * @return {Observable<any>}
+   */
+  @Cordova({ observable: true })
+  initSessionWithCallback(): Observable<BranchIoPromise> {
+    return;
+  }
+
   /**
    * Set Request Metadata
    * @return {Promise<any>}