[Key Vault] Move one Key Vault package to use core-rest-pipeline

[sadasant]

This issue is to track moving all of the 4 Key Vault packages to use core-rest-pipeline.

Maor and I should be able to divide and conquer.

We’ll add more details over the following weeks.

I’m making this “blocking-release” since core-rest-pipelines is counting on this to confirm the public API shape is good for Key Vault.

[ramya-rao-a]

Isnt this already covered in #14305?

[sadasant]

@ramya-rao-a that is correct! I’ve closed: #15522 since I prefer how this one is phrased, and the description.

[maorleger]

For July we're only moving one (other 3 are stretch depending on how that goes) - I will update this issue and create a separate issue for the other KV packages.