feat: Add SNAT property to firewall resources

[oZakari]

Overview/Summary

Add SNAT property to firewall resources

Related Issues/Work Items

Closes #739

This PR fixes/adds/changes/removes

1. Add SNAT property to firewall resources

Breaking Changes

None

Testing Evidence

Replace this with any testing evidence to show that your Pull Request works/fixes as described and planned (include screenshots, if appropriate).

As part of this Pull Request I have

• [x] Read the Contribution Guide and ensured this PR is compliant with the guide
• [x] Ensured the resource API versions in .bicep file/s I am adding/editing are using the latest API version possible
• [x] Checked for duplicate Pull Requests
• [x] Associated it with relevant GitHub Issues
• [x] (ALZ Bicep Core Team Only) Associated it with relevant ADO Items
• [x] Ensured my code/branch is up-to-date with the latest changes in the main branch
• [x] Performed testing and provided evidence.
• [ ] Updated one or more of the following tests (if required)
  • Unit
  • Linting
  • E2E (End-To-End)
  • ValidateAzCloud (Base validation in Azure Cloud)
  • ValidateMcCloud (Base validation in Azure China Cloud)
• [ ] Updated relevant and associated documentation (e.g. Contribution Guide, Module READMEs, Wiki Docs etc.)
• [ ] If relevant, created or updated Code Tours here

[oZakari]

/azp run validateazcloud

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[oZakari]

/azp run validateazcloud

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).