Use Nomad jobs as runners instead of allocations

As we can't control which allocations are destroyed when downscaling a job, we decided
to use Nomad jobs as our runners. Thus for each runner we prewarm for an environment,
a corresponding job is created in Nomad. We create a default job that serves as a template
for the runners. Using this, already existing execution environments can easily be restored,
once Poseidon is restarted.

api/websocket.go

@@ -128,7 +128,9 @@ type webSocketProxy struct {
 
 // upgradeConnection upgrades a connection to a websocket and returns a webSocketProxy for this connection.
 func upgradeConnection(writer http.ResponseWriter, request *http.Request) (webSocketConnection, error) {
-	connUpgrader := websocket.Upgrader{}
+	connUpgrader := websocket.Upgrader{CheckOrigin: func(r *http.Request) bool {
+		return true
+	}}
 	connection, err := connUpgrader.Upgrade(writer, request, nil)
 	if err != nil {
 		log.WithError(err).Warn("Connection upgrade failed")