Introduce Private Endpoint deployment were possible

[AlexanderSehr]

To implement best practices, we should deploy resources like Private Endpoints, Network Security Groups for Subnets, etc. where possible - and allow their configuration.

cc: ChrisSidebotham-MSFT (@ChrisSidebotham)

[AlexanderSehr]

Started working on this in my personal fork and introduced several major improvements (also structurewise). However, to finish the Pull Request, issue Azure/bicep#6540 must be resolved first as the Deployment Scripts can currently not communicate with Private Resources.