[ Azure CDN ] New cmdlets to support new AFD SKUs

[jorinmejia]

Description

This PR introduces new cmdlets which will support the CRUD operations of the new AFD SKUs (Premium / Standard Azure Front Door). Only new cmdlets are introduced. Exisiting cmdlets are left as is and do not interact with the new cmdlets.

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)
    • https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/868
  • the markdown help files have been regenerated using the commands listed here

[wyunchi-ms]

Please fix the Analysis issue and test cases.