azuread_application: avoid update after create

[manicminer]

There are a set of small bugs which can occur by updating immediately after creating an application, mostly around the reliance on d.GetChange(), which is always true in this scenario.

This PR refactors the update logic for the app_role and oauth2_permissions properties into a helper function, and stops returning applicationResourceUpdate() at the end of applicationResourceCreate(). Additionally fixes up the setting of prevent_duplicate_names on read to avoid unwanted diffs, and adds regression test coverage for that attribute.

Sets ConfigMode: schema.SchemaConfigModeAttr on the app_role attribute to enable specifying an empty list in order to remove existing app roles. As with the other optional+computed attributes, this only works on update and if a config change is detected. Test also amended for this case.

Resolves #364

[jackofallops]

Thanks @manicminer - LGTM 👍

[manicminer]

Linters passing locally

Acceptance test results:

[ghost]

This has been released in version 1.1.1 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azuread" {
    version = "~> 1.1.1"
}
# ... other configuration ...

[ghost]

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