Introducing Az.Security Assessment cmdlets

[chlahav]

Description

Adding various cmdlets to list and manage assessments related resources in Microsoft.Security RP (Az.Security)

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

[VeryEarly]

Hi @chlahav ,

Do you have approved design? If yes please attach the link, if not, please raise a new design

[chlahav]

hi @VeryEarly , we do have an approved design here

[VeryEarly]

hi @VeryEarly , we do have an approved design here

Sorry totally forgot I did that, will review this PR soon.

[azure-pipelines]

Pull request contains merge conflicts.

[VeryEarly]

please check comments,
record new added scenario tests.
Because the SDK upgrade, it's likely some test cases need to be re-recorded.

Also please resolve merge conflict in order to enable CI checks