{ApplicationGateway} Include the possible value for Operator and Vari…

[navba-MSFT]

…able parameter

On this page:
https://docs.microsoft.com/en-us/powershell/module/az.network/new-azapplicationgatewayfirewallexclusionconfig?view=azps-7.5.0

It seems it would be useful to document the valid values for the -Variable and -Operator parameters

Fixes #18106

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)
    • {Please put the link here}
  • the markdown help files have been regenerated using the commands listed here

[navba-MSFT]

@MikhailTryakhov Could you please approve and merge this once you get a chance ? Thanks in advance.

[VeryEarly]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[navba-MSFT]

@VeryEarly Thanks for approving the request. Once the Tests succeeds, could you please merge this PR ?