Add cowboy_opts option

This option will allow setting Cowboy-specific options like
'max_keepalive' or 'timeout'.

deps/rabbitmq_web_stomp/src/rabbit_ws_sockjs.erl

@@ -36,6 +36,8 @@ init() ->
             {[{port, Port0}|TCPConf0], Port0}
     end,
 
+    CowboyOpts = get_env(cowboy_opts, []),
+
     SockjsOpts = get_env(sockjs_opts, []) ++ [{logger, fun logger/3}],
 
     SockjsState = sockjs_handler:init_state(
@@ -48,7 +50,7 @@ init() ->
     NbAcceptors = get_env(nb_acceptors, 100),
     cowboy:start_http(http, NbAcceptors,
                       TCPConf,
-                      [{env, [{dispatch, Routes}]}]),
+                      [{env, [{dispatch, Routes}]}|CowboyOpts]),
     rabbit_log:info("rabbit_web_stomp: listening for HTTP connections on ~s:~w~n",
                     ["0.0.0.0", Port]),
     case get_env(ssl_config, []) of

deps/rabbitmq_web_stomp/src/rabbitmq_web_stomp.app.src

@@ -9,6 +9,7 @@
          {tcp_config, []},
          {ssl_config, []},
          {nb_acceptors, 100},
+         {cowboy_opts, []},
          {sockjs_opts, []}]},
   {applications, [kernel, stdlib, rabbit, rabbitmq_stomp, cowboy, sockjs]}
  ]}.