Audit and complete bicepparam support across azd

[spboyer]

Context

Issue #2783 requested updating templates to use .bicepparam instead of parameters.json. While azd has partial .bicepparam support (bicep_provider.go detects and uses .bicepparam files, local_preflight.go supports them, tests exist in cli_test.go), a full audit is needed to ensure complete end-to-end support.

Current State

• bicep_provider.go has a bicepparamMode that detects <moduleName>.bicepparam files
• local_preflight.go supports .bicepparam for validation snapshots
• Functional test storage-bicepparam exists
• azd add recognizes main.bicepparam

Needed

• Audit all provisioning paths to ensure bicepparam works consistently
• Verify template init/scaffolding can generate .bicepparam files
• Update official templates to use .bicepparam where appropriate
• Document bicepparam usage

Related: #2783

[vhvb1989]

There's a technical blocker to support .bicepparam the same way we support params.json (see: #2783 (comment))

Happy to chat/talk more about it @spboyer

[anthony-c-martin]

If you have the need for Bicep to request structured input from the calling tool (azd in this case), the externalInput function is a new feature that might be interesting to look at: https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/bicep-functions-parameters-file#externalinput

It was originally designed for a Microsoft-internal tool, but in an intentionally tool-agnostic manner. This link has example usages, but is only accessible by Microsoft employees: https://aka.ms/bicep/ev2-integration. Here was the original spec for the feature: https://github.com/Azure/bicep-reps/blob/3f3f371bdf43ef59b2d15682655b92bba3cfdddb/active/0018-tooling-params-api.md