GetCertificateOperation should be removed

[pakrym]

And replaced with an operation constructor.

[heaths]

We've decided to cut this. There are other operations like canceling and deleting an LRO that the service supports that we feel are better exposed by the CertificateClient.

[pakrym]

We need to adjust the guidelines for this first. We can put cancel and delete on the operation type

[heaths]

I'll open a dependency issue then, but it wasn't just a matter of cancel and delete. I talked about this with @KrzysztofCwalina and @schaabs as well. Them passing the right CertificateClient in is problematic, and our other pseudo-LROs for delete and recover can't be recreated from some dedicated URI, thus making the experience inconsistent.

[heaths]

After offline discussion, moving back in for now. Still some things to discuss.

[heaths]

Talking offline with @pakrym, @KrzysztofCwalina, and @schaabs, instead we will:

• Keep GetCertificateOperation on CertificateClient
• Move CancelCertificateOperation and DeleteCertificateOperation to CertificateOperation as Cancel and Delete, respectively.

This makes getting existing certificate operations more discoverable based on our UX studies. This is predicated on whether it's possible for other languages, however.