docs: update oauth2_permission_scope documentation

[robertmarsal]

Fix field marked as optional that is in fact required. When trying to create this resource without the field the following error gets returned:

16:47:34.579 STDERR terraform: │ Error: Could not update application with object ID: "<redacted>"
16:47:34.579 STDERR terraform: │
16:47:34.579 STDERR terraform: │   with module.<redacted>.azuread_application.this,
16:47:34.579 STDERR terraform: │   on ../../../../../../modules/<redacted>/main.tf line 16, in resource "azuread_application" "this":
16:47:34.579 STDERR terraform: │   16: resource "azuread_application" "this" {
16:47:34.579 STDERR terraform: │
16:47:34.579 STDERR terraform: │ unexpected status 400 (400 Bad Request) with error: ValueRequired: Property
16:47:34.579 STDERR terraform: │ value is required but is empty or missing.
16:47:34.580 STDERR terraform: ╵
16:47:34.660 ERROR  terraform invocation failed in .

Once the field is provided the error no longer occurs. The field is also required in the UI as can be seen in the below screenshot

[jackofallops]

HI @robertmarsal - Thanks for this PR. Unfortunately the docs need to reflect the schema code, so the scheme for this property would also need to be updated. However, afaik, value is a conditionally required property, so I don't believe we can mark it as required. If you have links to docs on this, I'm happy to reconsider and help out on getting this change correct?

[robertmarsal]

Thanks Jack, if it's conditionally required it makes sense. I do not have any links for docs on this to justify it should be always required.