use correct image for certificates

The Gitlab package is using the wrong image for certificates.
Has

  certificates:
    image:
      repository: registry1.dso.mil/ironbank/gitlab/gitlab/cfssl-self-sign
      tag: 1.4.1

should be

  certificates:
    image:
      repository: registry1.dso.mil/ironbank/gitlab/gitlab/alpine-certificates
      tag: 13.8.0