feat: expose provider region lister

[intel352]

Refs GoCodeAlone/workflow#813.

Adds the optional IaCProviderRegionLister typed service so workflow admin surfaces can use provider-sourced Azure regions instead of the local fallback catalog.

Verification:

• GOWORK=off go test ./...

[Copilot]

Pull request overview

This PR adds support for the optional typed gRPC service IaCProviderRegionLister so the Workflow host/admin UI can ask the Azure IaC plugin for a region list instead of relying on a host-side fallback catalog.

Changes:

• Advertises workflow.plugin.external.iac.IaCProviderRegionLister in the plugin manifest.
• Implements ListRegions on azureIaCServer and adds coverage to ensure the service is registered and advertised.
• Updates github.com/GoCodeAlone/workflow (and related indirect deps) to a version that includes the new typed service.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
plugin.json	Advertises the new typed IaC region lister service in iacServices.
internal/region_lister.go	Adds ListRegions implementation returning a region list.
internal/region_lister_test.go	Adds tests for region listing, service registration, and manifest advertising.
internal/iacserver.go	Adds RegionLister unimplemented embed and compile-time interface guard.
go.mod	Bumps workflow dependency to a version that includes RegionLister.
go.sum	Updates sums for the dependency upgrades.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 1 comment.