If any response contains octet-stream, make response binary

[kfcampbell]

Fixes #5208.

If a response contains application/octet-stream as a response type, the Kiota-generated response type should be a binary one.

An concrete example of when this may happen: an API is migrating from hosting their own assets to returning redirects to a blob storage service, and they may return either a 302 Found and redirect to a URL that contains the asset, or the binary asset directly. For a standard consumer with redirects enabled, the end result is the same. For Kiota, generation needs to know to return binary content types. Currently Kiota will not do so and instead return void types.

[kfcampbell]

I'm struggling a bit to test this change. I initially thought that adding a test case to the existing function @baywet graciously linked me to in this thread would be sufficient:

kiota/tests/Kiota.Builder.Tests/ContentTypeMappingTests.cs

Line 81 in 857987e

public void GeneratesTheRightReturnTypeBasedOnContentAndStatus(string contentType, string statusCode, bool addModel, string acceptedContentType, string returnType)

I've experimented with the case of [InlineData("application/octet-stream", "302", false, "application/octet-stream", "binary")] with both variants of addModel (the boolean parameter), and continue getting void results:

[xUnit.net 00:00:00.93]     Kiota.Builder.Tests.ContentTypeMappingTests.GeneratesTheRightReturnTypeBasedOnContentAndStatusWithNullModelType(contentType: "application/octet-stream", statusCode: "302", addModel: False, acceptedContentType: "application/octet-stream", returnType: "binary") [FAIL]
  Failed Kiota.Builder.Tests.ContentTypeMappingTests.GeneratesTheRightReturnTypeBasedOnContentAndStatusWithNullModelType(contentType: "application/octet-stream", statusCode: "302", addModel: False, acceptedContentType: "application/octet-stream", returnType: "binary") [270 ms]
  Error Message:
   Assert.Equal() Failure: Strings differ
           ↓ (pos 0)
Expected: "binary"
Actual:   "void"
           ↑ (pos 0)
  Stack Trace:
     at Kiota.Builder.Tests.ContentTypeMappingTests.GeneratesTheRightReturnTypeBasedOnContentAndStatusWithNullModelType(String contentType, String statusCode, Boolean addModel, String acceptedContentType, String returnType) in /home/kfcampbell/github/dev/kiota/tests/Kiota.Builder.Tests/ContentTypeMappingTests.cs:line 230
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
   at System.Reflection.MethodBaseInvoker.InvokeWithManyArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

Upon debugging, I never even hit the else if (modelType is null) statement that triggers the relevant logic.

[baywet]

Thanks for the contribution!
You were almost there, there were in fact two blocks to update. I took the opportunity to refactor the duplication.