Make bookingService optional for single seller systems #233
Description
bookingService is currently required, however it is not relevant for bespoke single seller systems. It should therefore be recommended.
Note this also applies to dataset sites, as the certificates, test suite, and dataset site template are designed to not required bookingService in the dataset site. Additionally, it is possible that only hasCredential is present in bookingService within the dataset site, in the case that an agency-built booking system has a test suite certificate (as the bookingService is effectively anonymous in this case)