Have our rails containers wait the database to be up
The script for waiting for the db already exists in our rails containers
Here we use initContainers to run the script for sidekiq and unicorn.
Using the initContainer allows us to more finely control the readiness probe to apply to the container startup, rather then waiting for external services to be available.
We don't bother using an initContainer for the migration job, as it doesn't gain us that same benefit, and instead waiting for the database is just part of its startup.
Edited by DJ Mountney