RouteHandlerMiddleware unwieldy for endpoint-specific handling

[jamesross3]

Existing method signature:

type RouteHandlerMiddleware func(rw http.ResponseWriter, r *http.Request, reqVals RequestVals, next RouteRequestHandler)

When adding RouteHandlerMiddleware, the RouteSpec within RequestVals is difficult to use safely given the path template of a RouteSpec is a construction of:

• the server's configured context path
• other subrouter paths
• the path of the endpoint of interest

Upon my first attempt at writing a RouteHandlerMiddleware, ensuring I matched a specific endpoint proved challenging - I had to choose between either taking an implicit assumption on witchcraft-go-server's usage of the context-path configuration point (I guess this is a pretty safe assumption) or just matching the path using strings.HasSuffix. I am unsure if there's something a little more ergonomic to provide users here.

Separate issue: when used in conjunction with conjure-go generated server code, an additional snag is having to copy the string literal for the route from the generated server code. Perhaps a separate ergonomics improvement there is defining those string literal paths as exported constants in conjure-go-generated code