request help: rewrite the http request method,

[kongh]

Issue description

Environment

• APISIX Go Plugin Runner's version: v0.3.0
• APISIX version: 2.14.1
• Go version: go1.17.9 darwin/arm64
• OS (cmd: uname -a): Darwin x-Pro-2.local 20.5.0 Darwin Kernel Version 20.5.0: Sat May 8 05:10:31 PDT 2021; root:xnu-7195.121.3~9/RELEASE_ARM64_T8101 arm64

Question: I need rewrite the http request method, can you add the method r.SetMethod() just like r.SetPath().

Why:

• We have many apis using the PUT DELETE methods, and the client do not supported those methods, but only GET/POST methods.
• We consider that put extra header named X-HTTP-Method-Override, then , rewrite the method to this in go runner plugin.

Example: Client -> Method(POST) and X-HTTP-Method-Override: PUT -> Go Runner Plugin -> Method(PUT) -> Upstream

[soulbird]

Would you like to contribute?