[Compute] ProximityPlacementGroupId Update feature

[hyonholee]

Description

https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/431
('ColocationStatus' is not included in this PR, because of missing Swagger spec)

• Add ProximityPlacementGroupId parameter to the following cmdlets:
  • Update-AzAvailabilitySet, Update-AzVM, Update-AzVmss
• Change ProximityPlacementGroup parameter to ProximityPlacementGroupId parameter in New-AzVM and New-AzVmss.
  (ProximityPlacementGroup parameter is still supported as an alias)
• Update help message for VM and VMSS priority.

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

[hyonholee]

@wyunchi-ms I replied your questions. Please let me know if you have further concerns. Thanks.