Provide a command to use to test publish / subscribe #84
Description
When the bundle is installed, there's a lot of moving pieces to get it all working. Sentry has the same problem and their bundle provides a sentry:test command which pushed a fake event to Sentry, allowing you to see your config and keys are correct and working.
This bundle could do the same, provide a basic command to check your hub is operational, Symfony can reach it and can read from it / write to it. The same command could be used to both publish and subscribe (in another window). Alternatively, it could show a sample curl command to use to test using that.