Update EgressExtensibilityApp to publish for every targetable RID

[jander-msft]

The ExtensionResponse_Success and ExtensionResponse_Failure tests frequently fail when running for .NET runtimes that are Windows x86, musl, and ARM64 installations. The likely cause is that the apphost for the test application is build for x64 installations (and more specificallly, glibc x64 for Linux).

The app needs to be updated to publish for every targetable RID and these tests need to calculate which RID variant to use at test time.

Alternative is to change the app to not create the apphost, but then we'd lose coverage for the scenario where the extension provides a native executable; the alternative is not desirable.