[New Extension]: pg_jsonschema

### Is there an existing issue for this extension request?

- [x] I have searched for an existing issue, and could not find a duplicate request.

### Extension Name

pg_jsonschema

### Project Repository URL

https://github.com/supabase/pg_jsonschema

### Extension Website URL (Optional)

_No response_

### Short Description

The pg_jsonschema extension provides JSON Schema validation for PostgreSQL json and jsonb data types. It allows you to validate JSON documents against JSON Schema specifications directly within the database.

### Main LICENSE Link

https://github.com/supabase/pg_jsonschema/blob/master/LICENSE

### License Compliance

- [x] The extension's license (linked above) complies with the list of allowed licenses.

### Known Dependent Extensions

None

### Component Owner and Maintenance Commitment

- [x] I/My organization commit to becoming the Component Owner and maintaining the extension image in the future.

### Additional Notes (Optional)

This extension is written in Rust using the pgrx framework. The build requires the Rust toolchain, cargo-pgrx, cmake, clang, and libclang-dev as build-time dependencies. No additional OS-level runtime dependencies are needed. Currently targets PostgreSQL 18 on Debian bookworm and trixie.

### GitHub Handles of Component Owners

@elohmeier

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct