Run configure command provided by the server that confirms app config

If the command does not exist on the server, don't run it and continue
as usual. If the command exists, then run it and fail if it fails.

This allows the server to specify any sort of configuration loading and
application checking that it needs to do so extra features can be added
without extending serverside and synchronizing versions on the server
with features provided by the server.
Yeah. I think ENV is better for passing params than arguments in this case. We already use the same names for ENV vars for the hooks so it makes it more uniform. I'd like to eventually set all those vars for the entire script run but I'm trying to avoid a rabbit hole (I already went down that rabbit hole with this feature and I don't have a good enough plan for process-wide env vars yet so I'm punting).