Expose response metadata on the HTTP response

[flaki]

We currently have no way to access response metadata (status code, headers) in http.* runnable API calls, this limits some usecases such as makes it impossible to follow redirects.

JS & TS method calls return a HTTPResponse object which has methods for various output formats (binary, text, JSON), while Rust for example only produces a binary stream here.

JS (Javy) support is tracked in suborbital/javy#20