Add Bicep support

[nathaniel-msft]

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Add Bicep support to the repo.

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Create a manual setup to switch between terraform or bicep.

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

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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.