Option for staying running in compose with healthchecks for depends_on support

[BretFisher]

In compose 2.x files, depends_on can support a condition: service_healthy option to prevent the starting of a container until a dependency is healthy.

This could be used for volume seeding, where you list a vackup service in the compose file, that will auto-copy data to a new volume on startup, and the service that depends on that volume will only startup after the vackup image is marked healthy.