Introducing Az.Security SecurityTopology cmdlets

[ariklin]

Description

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

Design review: https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/613

[adxsdkps]

Can one of the admins verify this patch?

[VeryEarly]

• updated changelog, please only add new changes under upcoming release

• sorry I didn't identify this in the design, please use singularity for cmdlet name:
  Get-AzSecurityTopologies -> Get-AzSecurityTopology

• please fix failed test cases