Add CLI Support for Private Link for Key Vault

[ShaneBala-keyvault]

Resource Provider
What is the Azure resource provider your feature is part of?
Azure Key Vault

Description of Feature or Work Requested
Provide a brief description of the feature or work requested. A link to conceptual documentation may be helpful too.
Add CLI Support for Private Link for Azure Key Vault

Minimum API Version Required
What is the minimum API version of your service required to implement your feature?
See Swagger Doc Below

Swagger Link
Provide a link to the location of your feature(s) in the REST API specs repo. If your feature(s) has corresponding commit or pull request in the REST API specs repo, provide them. This should be on the master branch of the REST API specs repo.
Azure/azure-rest-api-specs#7631

Target Date
If you have a target date for release of this feature/work, please provide it. While we can't guarantee these dates,
it will help us prioritize your request against other requests.
End of November 2019

[yonzhan]

@jiasli planned in S162.

[bim-msft]

PR merged, will release on Feb 18.