get requestHeaders() {
    // Create the headers object.
    const headers = new Formio.Headers();

    // Add custom headers to the url.
    if (this.component.data && this.component.data.headers) {
      try {
        _.each(this.component.data.headers, (header) => {
          if (header.key) {
            headers.set(header.key, this.interpolate(header.value));
          }
        });
      }
      catch (err) {
        console.warn(err.message);
      }
    }

    return headers;
  }
Get the request headers for this select dropdown.
@returns {*} - Returns the request headers for this select dropdown.