Add workflow and tests

[jfaurskov]

Overview/Summary

Add workflow and test scripts to verify ARM templates updated based on https://github.com/Azure/arm-ttk. Described in https://dev.azure.com/CSUSolEng/Guidance%20-%20Observability/_workitems/edit/37410

This PR fixes/adds/changes/removes

1. Add .github/workflows/unit-test-arm-templates.yml to run whenever a PR is made updating one or more ARM templates
2. Add .github/actions/Test-Armtemplates.Tests.ps1 which does the actual testing.

Breaking Changes

No breaking changes.

As part of this Pull Request I have

• Read the Contribution Guide and ensured this PR is compliant with the guide
• Checked for duplicate Pull Requests
• Associated it with relevant GitHub Issues or ADO Work Items (Internal Only)
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Ensured PR tests are passing
• Updated relevant and associated documentation (e.g. Contribution Guide, Docs etc.)