getItems method
Will get a collection of PcoServicesItem objects (expecting many)
using a path like this: https://api.planningcenteronline.com/services/v2/series/1/plans/1/live/1/items
Implementation
Future<PcoCollection<PcoServicesItem>> getItems(
{PcoServicesItemQuery? query}) async {
query ??= PcoServicesItemQuery();
var url = '$apiEndpoint/items';
return PcoCollection.fromApiCall<PcoServicesItem>(url,
query: query, apiVersion: apiVersion);
}