Allow for deployment into air gapped environment

[KenFigueiredo]

Currently there is a hard requirement for the deploying CI/CD tool to have direct network access to the RDS / SQL DB during setup (via these scripts:

• https://github.com/ExpediaGroup/apiary-data-lake/blob/master/scripts/mysql-user.sh
• https://github.com/ExpediaGroup/apiary-data-lake/blob/master/scripts/db-iam-auth.sh)

This makes fully automated deployment into these environments impossible as you'd have to deploy up to the point of RDS creation for it to fail, then manually create the users and skip the terraform step.

One possible solution to deploying to these types of environments (in both ECS / K8S) would be to move those scripts to startup / init containers. The only downside to this approach that the init containers for apiary-rw & apiary-ro containers would need permission to the RDS / SQL DB root password to create their respective users.

This additionally has the additional benefit of resolving #119, where as the solution called out in the issue would still require a direct connection from the deployment tool.

I have a working PoC of this for ECS that I can open up as PR for this repo but haven't touched it at all on the Kubernetes deployment side.

[KenFigueiredo]

Fixed w/ merging of the linked PRs