Rdkafka runs in its own multiverse group

[tannalynn]

So this will make rdkafka run in it's own group for now. I named the group just kafka because i'd like to later include both kafka gems in it, but for now, for debugging our weird problems, I want it to only be rdkafka.

I also added the exit code to another string. We do already output the exit code in a different spot, but I wasn't seeing that message actually show up when we see our problem for some reason, so I've added it to a message that I do actually see, so maybe we'll get a little more info out of that.

Before:
"rdkafka" for Envfile entry 0 failed! 
Now
"rdkafka" for Envfile entry 0 failed! (exit: pid 9066 exit 1)

[github-actions]

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