[KeyVault] Support multi-regions and testing name availability

[BethanyZhou]

Description

Added a command called Test-AzKeyVaultNameAvailability by autorest.powershell

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

[azure-client-tools-bot-prd]

️✔️Az.Accounts

️✔️Build

️✔️PowerShell Core - Windows

⚠️Az.KeyVault

️✔️Build

️✔️PowerShell Core - Windows

️✔️Breaking Change Check

️✔️PowerShell Core - Windows

⚠️Signature Check

⚠️PowerShell Core - Windows

Type	Cmdlet	Description	Remediation
⚠️	Get-AzKeyVaultManagedHsmRegion	Get-AzKeyVaultManagedHsmRegion Changes the ConfirmImpact but does not set the SupportsShouldProcess property to true in the cmdlet attribute.	Determine if the cmdlet should implement ShouldProcess and if so determine if it should implement Force / ShouldContinue
⚠️	Get-AzKeyVaultManagedHsmRegion	Get-AzKeyVaultManagedHsmRegion changes the confirm impact. Please ensure that the change in ConfirmImpact is justified	Verify that ConfirmImpact is changed appropriately by the cmdlet. It is very rare for a cmdlet to change the ConfirmImpact.

️✔️Help Example Check

️✔️PowerShell Core - Windows

️✔️Help File Existence Check

️✔️PowerShell Core - Windows

⚠️File Change Check

⚠️PowerShell Core - Windows

Type	Cmdlet	Description	Remediation
⚠️		It is required to update ChangeLog.md if you want to release a new version for Az.KeyVault.	Add a changelog record under Upcoming Release section with past tense.

️✔️UX Metadata Check

️✔️PowerShell Core - Windows

⚠️Test

⚠️ - Linux

Type	Title	Current Coverage	Description
⚠️	Test Coverage Less Than 50%	5.81 %	Test coverage for the module cannot be lower than 50%.

⚠️ - MacOS

Type	Title	Current Coverage	Description
⚠️	Test Coverage Less Than 50%	5.81%	Test coverage for the module cannot be lower than 50%.

⚠️PowerShell Core - Windows

Type	Title	Current Coverage	Description
⚠️	Test Coverage Less Than 50%	5.81%	Test coverage for the module cannot be lower than 50%.