Update IaC to generate multiple app registrations

#### Describe Problem

Currently, we use the same app registration / client id for the API and the front-end.
Since these two are different clients with different concerns, it is recommended to havve separate app registrations for the different applications / clients.

Some issues that show up when using a single app registration:
- The API does not need reply urls or the OpenID Connect scopes
- The front-end is a public client (until #391 is implemented), but the API is a confidential client
- The API may need additioanl scopes / API-permissions to call different services, which are not intended to be called directly from the front end

#### Suggest Solution

Create different app registrations (via bicep) for the different components (and environments)

#### Additional Details