Emit stop error event on client and server timeout

[binaryseed]

When the client making a request hangs up (ex: client timeout), cowboy detects this and executes the terminate stream handler callback with

Reason = {socket_error, closed, 'The socket has been closed.'}

When the server reaches the idle_timeout, cowboy executes the terminate stream handler callback with

Reason = {connection_error, timeout, 'Connection idle longer than configuration allows.'}

This PR emits a [cowboy, request, stop] event with an error instead of a response in that situation, since no response is ever sent to the client.

[binaryseed]

• Adopted the done idea to prevent double events in race conditions
• Handle case when the server closes the request due to idle_timeout as well (so now client & server timeouts are handled)
• Quick refactor to pull telemetry:exception calls into functions