Accelerated upload route for conan package files

In this MR we add two endpoints for proxying requests
to services running inside the runner's builds.

One of the endpoints is for regular HTTP requests, while
the other is for websockets.

We're moving from using terminology related to terminal when
we refer to websockets connections. It's more generalistic
a concept like channel.

This is a necessary change to solve a security issue. For more details,
see this issue: https://gitlab.com/gitlab-org/gitlab-workhorse/issues/197

This reverts merge request !267

This reverts merge request !265

Apply `instrumentDuration()` to both `route()` and `wsRoute()`.

Add instrumentation middleware function to produce histograms per
route/method.

This reverts commit bba7d53e, reversing
changes made to 815be1cc.

A GitLab environment may expose a terminal connection for out-of-band access.
Workhorse is responsible for providing a websocket connection to the terminal
if present.

It authenticates the user and retrieves connection details from GitLab using
the environments/:id/terminal.ws/authorize endpoint, and sets up a proxy to
the terminal provider, converting from the remote's subprotocol to a common
format.

Authentication is periodically re-done, and the connection will be broken if
it fails, or if the connection details change in any way.

Expose three options to configure queueing limits:
- apiLimit
- apiQueueLimit
- apiQueueTimeout