Adding extra containers to deployments

When using an external database, it's common to have to use a proxy to safely connect from a service to the database. In Google Cloud, one of the recommended approaches is to have a side car container of cloud-sql-proxy.

I am deploying Devlake in a GitOps Flux-based environment, so `Kustomize` is not an option as it executes before the Helm chart is extracted and applied. Helm post renderers are an option, but some good effort to get it working.

Additionally, enabling extra containers can also enable other use cases.