Add support event hooks

[eznix86]

It would be nice to have a custom event hooks for a custom script somewhere in the project.

Sort of like in the nginx:

exec_publish /custom/script/streamHasStarted.sh;
exec_publish_done /srv/nginx/youAreNowLive.sh;

[eznix86]

we could do the setup like you did, only from the docker-compose.yml file.
As such:

CMD_TO_EXEC_ON_PUBLISH:  "/custom/script/streamHasStarted.sh"
CMD_TO_EXEC_ON_PUBLISH_COMPLETE:  "/custom/script/youAreNowLive.sh"