images/git: Build for s390x

[deepsm007]

This commit adds a Google Cloud Build definition for building git
s390x images and pushing them as a manifest list together with their
s390x counterparts.

Blocked on: #23412

/cc @stevekuznetsov

rel: #16588

[k8s-ci-robot]

Hi @deepsm007. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[spiffxp]

/ok-to-test
/approve
/lgtm

[deepsm007]

/hold

[deepsm007]

/assign @fejta

[mkumatag]

/lgtm

I see a s390x image here:

$ docker manifest inspect gcr.io/k8s-prow/alpine:v20211015-92dc282
{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 738,
         "digest": "sha256:663b7c269935803798213094965c206d047db6b0b0f379262de4ac819e4b69d9",
         "platform": {
            "architecture": "amd64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 738,
         "digest": "sha256:9043c54f45c5a862829e905456592379daa503d4e45c6c5a7b85ce8c78932bce",
         "platform": {
            "architecture": "arm64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 738,
         "digest": "sha256:f6126f28635079aa8e8585ec52fbc0be5fcdd1c5ae945f79554de4108bd65c5e",
         "platform": {
            "architecture": "ppc64le",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 738,
         "digest": "sha256:0b7ea572e118259458f2a943bd1f6d007c4c272bfae7fb04238291e1d004085f",
         "platform": {
            "architecture": "s390x",
            "os": "linux"
         }
      }
   ]
}

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deepsm007, mkumatag, spiffxp

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[deepsm007]

/unhold