[KeyVault] Selective restore key for a managed hsm backup

[BethanyZhou]

Description

Target:
To support selective restoring a key vault key from a managed HSM full backup.

Change:
Added a parameter called KeyPath into all parameter sets.

Logic:
If KeyPath is null, conduct full back-up restore. Otherwise only restore a key.

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)
    • {Please put the link here}
  • the markdown help files have been regenerated using the commands listed here

[BethanyZhou]

/azp run azure-powershell - powershell-core

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[wyunchi-ms]

Please resolve the conflicts. @BethanyZhou

[BethanyZhou]

@wyunchi-ms Resolved. Please help to review again, thanks.