Add timeouts to request handling

[divergentdave]

We may want to add timeouts to cancel request handling futures in addition to cancelling on disconnect (see #3033). It would make sense to set the timeout in Janus slightly shorter than the timeouts of any reverse proxies in front of it. Note that there are some situations, depending on the client, the HTTP protocol version, the OS, and when and how the disconnection happens, that may mean our server can't detect a disconnection.