[http server]: health_api is rather confusing because it's not exclusive for /health

[niklasad1]

#763 (comment)

Additionally the API is quite easy to misuse if one passes in something like a path with / and similar.

[tarrencev]

I think it makes sense to allow arbitrary registration of get hooks. Kubernetes for example supports both a ready and live endpoint and a consumer might want to expose metrics through another path too.

[jsdw]

We're hoping that, now we support tower middleware on the HTTP server, that we might be able to remove this /health stuff from the core jsonrpsee code and provide it as a piece of middlewhere instead which might look like (names all made up):

let layer = ProxyGetRequestLayer::new("/health", "health_rpc_call");

And internally this middleware would look for matching HTTP requests and convert them into jsonrpc requests to pass on, and then strip the jsonrpsee outer stuff from the response too before passing it back.