create method
      
Future<AccountCredentials> 
create(
    
- AccountCredentials request,
 - String accountId, {
 - String? $fields,
 
Uploads credentials for the Merchant Center account.
If credentials already exist for this Merchant Center account and purpose, this method updates them.
request - The metadata request object.
Request parameters:
accountId - Required. The merchant id of the account these credentials
belong to.
$fields - Selector specifying which fields to include in a partial
response.
Completes with a AccountCredentials.
Completes with a commons.ApiRequestError if the API endpoint returned an error.
If the used http.Client completes with an error when making a REST call,
this method will complete with the same error.
Implementation
async.Future<AccountCredentials> create(
  AccountCredentials request,
  core.String accountId, {
  core.String? $fields,
}) async {
  final body_ = convert.json.encode(request);
  final queryParams_ = <core.String, core.List<core.String>>{
    if ($fields != null) 'fields': [$fields],
  };
  final url_ =
      'accounts/' + commons.escapeVariable('$accountId') + '/credentials';
  final response_ = await _requester.request(
    url_,
    'POST',
    body: body_,
    queryParams: queryParams_,
  );
  return AccountCredentials.fromJson(
      response_ as core.Map<core.String, core.dynamic>);
}