Adding schedule fields to NewAzMaintenance Configuration cmdlet and new Public Configuration GET cmdlet

[sotaneja]

Description

Adding new GET cmdlet for new resource type public maintenance configurations
Adding optional schedule related fields for New-AzMaintenanceConfiguration cmdlet

Design Review: https://github.com/Azure/azure-powershell-cmdlet-review-pr/issues/693

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

[adxsdkps]

Can one of the admins verify this patch?

[isra-fel]

Target                                  Description
  ------                                  -----------
  Get-AzMaintenancePublicConfiguration.md Online version in the header of the file is incorrect. The corresponding URL s.

Please fix the URL issue in docs

[isra-fel]

• Az.Maintenance.md needs also to be updated because of newly introduced cmdlet.

[isra-fel]

@sotaneja please never add any ## Version x.y.z title in ChangeLog.md. Just put your change logs beneath Upcoming Release.

I updated it for you but please be careful about it next time.

THanks!