Scaffolds the coderd/templatebuilder package for the guided template
builder (DEVEX-272). Adds:
- codersdk.TemplateBuilderModule and related types matching the RFC schema
- ModuleManifest internal type with go:embed wiring for bundled catalog
- LoadModules() to parse module.json files from embedded FS
- ToSDK() conversion from on-disk manifest to API response type
- Stub module exercising all schema fields (builder_managed, sensitive,
conflicts_with, compatible_os, pinned_version)
- Tests for catalog loading, field parsing, and SDK conversion
Jeremy Ruppel