Rename HttpMiddleware/WsMiddleware to avoid confusion

[jsdw]

"Middleware" is a term that has some certain meaning/connotations around being able to intercept and modify requests/responses. The things that we call middleware have no ability to effect the requests/responses and really just exist as hooks for metrics and logging purposes.

Let's call it something like RpcMetrics or what have you. This leaves the door open for "real" middleware, too, at some point in the future.