feat: added support for creating a service prinicpal for the application

[SanderBlom]

Added support for optionally creating a service principal when creating an application

Description

This should give us the option to create a service principal (Enterprise application) in the applications block

Fixes #136

Type of Change

• [ ] Bug fix
• [x] New feature
• [ ] Documentation update
• [ ] Other

Testing

See the testing docs for more information about how to test your code

• [x] Performed a local terraform plan, apply, and destroy to validate changes.
• [x] All tests are passing.
• [x] Added, updated, or removed tests when appropriate

Checklist

Before submitting this PR, please ensure the following:

• [ ] My commits follow the Conventional Commits style guide
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings. I have ran terraform validate in the root module and all sub modules where I have made changes

Additional Information

Provide any additional information or context about the pull request here.

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[SanderBlom]

Det ser ut til at man kun kan opprette en Enterprise Application slik det er lagt opp nå - jeg tenker vi like gjerne kan støtte flere (hvis det er mulig).

Ser ikke ut som det er mulig å ha en-til-mange forhold mellom applikasjoner (app registrations) og service principals (enterprise applications).

Når jeg laget et map med to objecter så får jeg denne feilmeldingen:

│ Error: Could not create service principal
│ 
│   with module.station-applications.module.applications["maximum"].azuread_service_principal.sp["maximum"],
│   on ../application/azuread_application.tf line 126, in resource "azuread_service_principal" "sp":
│  126: resource "azuread_service_principal" "sp" {
│ 
│ ServicePrincipalsClient.BaseClient.Post(): unexpected status 409 with OData error:
│ Request_MultipleObjectsWithSameKeyValue: The service principal cannot be created, updated, or restored because the
│ service principal name b1712237-5c04-4016-97bd-707613ae404e is already in use.
╵

@kimfy