feat(argo-workflows): Add support for extra containers in server & controller deployment

[mikebryant]

My use-case for this is using persistence with a GCP CloudSQL database, using the sidecar pattern for the cloud-sql-proxy

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Checklist:

• I have bumped the chart version according to versioning
• I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• Any new values are backwards compatible and/or have sensible default.
• I have signed off all my commits as required by DCO.
• My build is green (troubleshooting builds).

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[mikebryant]

Some basic testing:

mikebryant@BULB-MB-0246 argo-workflows % cat env.yaml
server:
  extraContainers:
    - name: blah
      image: blah
mikebryant@BULB-MB-0246 argo-workflows % helm template . --values env.yaml | tail
          - name: tmp
            mountPath: /tmp

        - image: blah
          name: blah
      volumes:
      - name: tmp
        emptyDir: {}
      nodeSelector:
        kubernetes.io/os: linux

[mikebryant]

Thanks for the review, have applied the requested changes :)

[oliverbaehler]

lgtm, @mikebryant Thanks for your contribution.