Update Azure Firewall Network Rules documentation

[fanymanea]

Description

The only forms accepted by AzFw cmdlets for Network protocols are TCP and UDP (all caps). Update documentation to include valid examples.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• 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:
  • the changes have gone through a cmdlet design review
  • the cmdlet markdown files were generated using the platyPS module

[praries880]

@fanymanea do you intend these changes to go to the October branch for network or is preview the correct place to merge the changes in?

[fanymanea]

@praries880
This documentation correction is for current version, not for something we will introduce in October. I believe the right target is preview. What do you think?