BackendSrv: support binary responseType like $http did (#29004)

packages/grafana-runtime/src/services/backendSrv.ts

@@ -61,6 +61,15 @@ export type BackendSrvRequest = {
    */
   params?: Record<string, any>;
 
+  /**
+   * Define how the response object should be parsed.  See:
+   *
+   * https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Sending_and_Receiving_Binary_Data
+   *
+   * By default values are json parsed from text
+   */
+  responseType?: 'json' | 'text' | 'arraybuffer' | 'blob';
+
   /**
    * The credentials read-only property of the Request interface indicates whether the user agent should send cookies from the other domain in the case of cross-origin requests.
    */