Provide Warning Messages For Azure KeyVault Soft Delete

[BethanyZhou]

Description

The ability to create new key vaults with soft delete disabled will be deprecated by December 2020. Hence, all key vault will enable soft delete mandatory and some breaking changes will be introduced.

Parameter DisableSoftDelete in New-AzKeyVault and EnableSoftDelete in Update-AzKeyVault will be removed. Besides, deleting keys, certificates and secrets will be affected as well. So we are going to provide warning messages for these situations.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate ChangeLog.md file(s) has been updated:
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header -- no new version header should be added
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • a cmdlet design review was approved for the changes in this repository (Microsoft internal only)
  • the markdown help files have been regenerated using the commands listed here

[adxsdkps]

Can one of the admins verify this patch?

[isra-fel]

/azp run azure-powershell - powershell-core

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[isra-fel]

Please resolve the conflicts. Thanks

[BethanyZhou]

Conflicts have been solved. Please help to review, thanks.

[isra-fel]

LGTM