create method
Creates a new channel.
Returns the newly created channel if successful.
request - The metadata request object.
Request parameters:
advertiserId - The ID of the advertiser that owns the created channel.
Value must have pattern ^\[^/\]+$.
partnerId - The ID of the partner that owns the created channel.
$fields - Selector specifying which fields to include in a partial
response.
Completes with a Channel.
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<Channel> create(
  Channel request,
  core.String advertiserId, {
  core.String? partnerId,
  core.String? $fields,
}) async {
  final body_ = convert.json.encode(request);
  final queryParams_ = <core.String, core.List<core.String>>{
    if (partnerId != null) 'partnerId': [partnerId],
    if ($fields != null) 'fields': [$fields],
  };
  final url_ =
      'v3/advertisers/' + core.Uri.encodeFull('$advertiserId') + '/channels';
  final response_ = await _requester.request(
    url_,
    'POST',
    body: body_,
    queryParams: queryParams_,
  );
  return Channel.fromJson(response_ as core.Map<core.String, core.dynamic>);
}