[KeyVault] Regenerate @azure/keyvault to address customer issues

[daviwil]

This change regenerates the @azure/keyvault library using autorest.typescript 4.2.3 so that it picks up ms-rest-js 2.0. This change is needed to alleviate some customer reported issues with that library. We'll also be deprecating this library after the hotfix update.

Tasks

• Verify that issues [KeyVault] Update @azure/ms-rest-azure-js to 2.0.0 in @azure/keyvault #4530 and [KeyVault] - Types of property signRequest are incompatible (outdated ms-rest-js 1.0 reference) #4793 are fixed with this change
• Deprecate the @azure/keyvault package with the command npm deprecate @azure/keyvault "This package is deprecated. Please use @azure/keyvault-keys and @azure/keyvault-secrets instead."

[daviwil]

This hotfix may not actually be necessary:

• I could not reproduce the original issue in [KeyVault] Update @azure/ms-rest-azure-js to 2.0.0 in @azure/keyvault #4530 with @azure/keyvault 1.0 (likely due to fixes made to ms-rest-js in June)
• Issue [KeyVault] - Types of property signRequest are incompatible (outdated ms-rest-js 1.0 reference) #4793 was caused by a user upgrading ms-rest-js to 2.0 when this library does not support it

I think we should hold off on merging this PR and shipping the hotfix until we determine that it's necessary.

[ramya-rao-a]

We also need a message on the top of the readme talking about the deprecation and pointer to the new libraries.

Go ahead and merge the PR. Will share the wording for the message and we can do that in a separate PR

[ramya-rao-a]

The @azure/keyvault package has been officially deprecated with relevant deprecation message. We also don't have the package as part of this repo anymore. Therefore, this PR is no longer needed