Provide metric attribute to see max number of concurrently active sessions for deployment

/deployment=helloworld.war/subsystem=undertow:read-attribute(name=max-active-sessions)

            "max-active-sessions" => {
                "type" => INT,
                "description" => "The maximum allowed number of concurrent sessions that this session manager supports",
                "expressions-allowed" => false,
                "nillable" => false,
                "access-type" => "metric",
                "storage" => "runtime"
            },