Prepare release 0.7.3

[stevenbal]

Make a release that includes #37 and upgrade to this new versions in the components that use this configurationstep

• Open Zaak
• Open Notificaties ⬆️ Upgrade notifications-api-common to 0.7.3 open-zaak/open-notificaties#296
• Objects API ⬆️ Upgrade notifications-api-common to 0.7.3 objects-api#623
• Open Klant ⬆️ Upgrade dependencies open-klant#444
• Open Product? (double check if it uses this step) ⬆️ Upgrade notifications-api-common to 0.7.3 open-product#165

[Floris272]

#47 could be included as well.