Setup commands that run in a different container

[charleskorn]

Continuation of discussion in #105, for the more advanced use case:

some way to run commands in another container after another container becomes healthy but before any containers that depend on it start

[paulvalla-zorro]

That would be handy, we are trying to initialize a dynamodb running in one container, using an aws-cli container to create a table and once everything is ready, run integration tests in a third container.

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[kokrange]

I think it's a pretty common scenario especially for database migration because most db containers do not have the environment(migration tools) to migrate itself. It would be nice to have some kind of short-lived container that do something only for the long-lived container and quit after finished, like k8s Jobs.