Credo checks for process propagation

[danschultzer]

We've implemented custom credo check to ensure that Task (and LiveView async in #439) process propagation wappers are used. This prevents engineers from deploying code that doesn't propagate context. The problem is that you won't know this is an issue until you look at the traces and discover that they are detached. Would this be a useful utility library in this repo? I can also maintain my own repo for this, but in either case would like it on hex as we have a bunch of Elixir deployments that all need it.