Add CodeQL security scanning & What-If reliability flag

[Gordonby]

PR Summary

Adding code scanning

Discover vulnerabilities across a codebase with CodeQL
https://codeql.github.com/

Azure CLI What-If reliability

Leveraging a repo level secret variable, to continue on error for the What-If step (see comment).
Having it at the Repo level will let us more easily toggle it, and since this isn't the first time is halted builds - we need to do it easily.

ERROR: InternalServerError - Encountered internal server error while processing the deployment what-if request.

PR Checklist

• PR has a meaningful title
• Summarized changes
• This PR is ready to merge and is not Work in Progress
• Link to a filed issue

[Gordonby]

I've added this to 2 of the actions because What-If steps are failing with an "internal server error" on AZ CLI 2.30.0 and 2.31.0

        continue-on-error: ${{ secrets.ISAZCLIWHATIFUNRELIABLE == 'true' }}

ref: Azure/azure-cli#19850

[JimPaine]

Looks good to me. I would probably have liked the idea of handling the error differently :D but looking through the referenced issue a fix is on the way so this is great.