EES-5952 Add infrastructure for Event Grid custom topics

[benoutram]

This PR adds the Bicep infrastructure to create Event Grid custom topics.

These topics will be used to publish events to Event Grid by Admin and Publisher when certain conditions are met.

Below is an explanation of when each topic will be used.

Publication changed topic

• When a publication is changed e.g. a change to the publication title or summary.
• When the latest published release of a publication is changed after altering the publication's release order.

Theme changed topic

• When a theme is changed e.g. a change to the theme title.

Release changed topic

• When a release is changed e.g. a change to the release label.

Release version changed topic

• When a new release version is published

Publishing events to the topics in each of the above scenarios has been the work of EES-5954, EES-5962, EES-5953, EES-5908, EES-5955 and EES-5956.

[leeoades]

I've made some minor comments that might be way off due to my lesser knowledge of the bicep goodness - so I've approved to leave in your capable hands.