Support author-provided schemas for PowerShell adapted resources #1814

Summary of the new feature / enhancement

Follow-up to #1775: generated metadata cannot fully describe custom PowerShell resource representations. Resource authors should have an explicit mechanism to provide their own JSON schema for an adapted resource.

Proposed technical implementation details (optional)

Define and document the module/resource metadata contract before implementation, including how an author schema is located, validated, cached, and invalidated. Specify precedence versus generated schemas, relative-reference resolution, and compatibility with canonical input/output names and export filtering. Exercise both PowerShell adapters with author-provided schemas and actionable diagnostics for missing or invalid schemas.