feat: Add Extra Containers Support

[crhuber]

Adds support for extra containers to be added to the deployment. This is useful where teams have a need to add a sidecar container alongside the main application.

For example to use GCP CloudSQL you need to use cloudsqlproxy.
Usage would be like so

  extraContainers:
    - name: cloud-sql-proxy
      image: gcr.io/cloud-sql-connectors/cloud-sql-proxy:2.1.2-alpine
      imagePullPolicy: IfNotPresent
      command:
        - "./cloud-sql-proxy"
        - "foo:europe-west1:bar"
        - "--port"
        - "5432"
        - "--structured-logs"
      ports:
        - containerPort: 5432
          protocol: TCP
        runAsNonRoot: true
      resources:
        limits:
          memory: 48Mi
        requests:
          cpu: 100m
          memory: 32Mi

[CLAassistant]

All committers have signed the CLA.

[crhuber]

Hey @dlen any chance of a review here please? thanks

[dlen]

hi @crhuber!

Thanks for your submission it is really appreciated! I'll merge this week!

[andmich351]

Hey @dlen, would you maybe have some updates regarding merging this change?

[ngoduykhanh]

@dlen any news? I am looking forward to using this feature too 🙇

[dlen]

Sorry guys I had some other priorities these last few weeks. @Tecnobutrul is taking care of this and other PR to make a release ASAP.