Add Bicep support

[nathaniel-msft]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Add Bicep support to the repo.

Describe the solution you'd like A clear and concise description of what you want to happen.

Create a manual setup to switch between terraform or bicep.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

We thought of making a new repo, but it's difficult to maintain and results in desynced content.

Additional context Add any other context or screenshots about the feature request here.

This will be used in AKS Docs on Learn.

[jongio]

1. Move tf files to /infra/terraform
2. Put bicep files in /infra/bicep
3. Update azure.yaml to use terraform by default
4. Add new azure-bicep.yaml file to root of repo.
5. Add readme note that they need to rename the azure-bicep.yaml file to azure.yaml to use bicep.