feat: add method opt to overwrite http method

[psteinroe]

adds a method opt to overwrite the http method of the request that is being sent to the target.

use case is that the target may only support a POST request, for example because it does not confirm to certain standards, but the proxy should expose the same endpoint as PATCH. with the method parameter set to POST, the incoming PATCH request is forwarded as POST.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[psteinroe]

lgtm

Thanks! Anything left to do so this can be merged and released?