Images/git: Build for ppc64le

[deepsm007]

This commit adds a Google Cloud Build definition for building git
ppc64le images and pushing them as a manifest list together with their
ppc64le counterparts.

Blocked on: #23276

/cc @mkumatag
/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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[mkumatag]

/lgtm
/hold
/ok-to-test
hold until #23276 merges

[alvaroaleman]

/assign @chaodaiG

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chaodaiG, deepsm007

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[mkumatag]

@deepsm007 please squash the commits

[mkumatag]

/lgtm
/unhold

[mkumatag]

now we have a new image with ppc64le

$ manifest-tool inspect gcr.io/k8s-prow/git:v20210819-42fed69
Name:   gcr.io/k8s-prow/git:v20210819-42fed69 (Type: application/vnd.docker.distribution.manifest.list.v2+json)
Digest: sha256:dfe311e5d8f01035654611895bd3be43e28253cf96d2c3ab4bb0a795fa9d5a63
 * Contains 3 manifest references:
1    Mfst Type: application/vnd.docker.distribution.manifest.v2+json
1       Digest: sha256:3fef8233c73aa85f953f0f90a3dc0daee88b2eea5210af0779512c34ce5f1ae6
1  Mfst Length: 949
1     Platform:
1           -      OS: linux
1           - OS Vers:
1           - OS Feat: []
1           -    Arch: amd64
1           - Variant:
1           - Feature:
1     # Layers: 3
         layer 1: digest = sha256:29291e31a76a7e560b9b7ad3cada56e8c18d50a96cca8a2573e4f4689d7aca77
         layer 2: digest = sha256:d8b0fef36ee8776d54c12fed24e6eae5e3ad0253ca18dca4e57e90f1d5c85eda
         layer 3: digest = sha256:2ca59ef288e1fcd8e2d6b3d4eb17807adfb38d42a4b69f49a59be159eb86d119

2    Mfst Type: application/vnd.docker.distribution.manifest.v2+json
2       Digest: sha256:17373d3456b4ad146b42b23fd4b6322dc804b62af6c3f939fbf7533239d2dce5
2  Mfst Length: 949
2     Platform:
2           -      OS: linux
2           - OS Vers:
2           - OS Feat: []
2           -    Arch: arm64
2           - Variant:
2           - Feature:
2     # Layers: 3
         layer 1: digest = sha256:fd3acdcea5682abced546ec19fb6ebee725c5184e5d91614c469c0a79e67f2d0
         layer 2: digest = sha256:c870bdb2572e9e2969fa459f01b8acf3a69083113b44c807043920679525b54a
         layer 3: digest = sha256:e0ed68c040143e3d054c685324ed2f5adf1ac650c19dbf172beedd0b920fbc88

3    Mfst Type: application/vnd.docker.distribution.manifest.v2+json
3       Digest: sha256:cc5b28dfc4165dccc91d0cf04e9addf1b2d22ab70b9a5e313b6299a4aa1d6646
3  Mfst Length: 949
3     Platform:
3           -      OS: linux
3           - OS Vers:
3           - OS Feat: []
3           -    Arch: ppc64le
3           - Variant:
3           - Feature:
3     # Layers: 3
         layer 1: digest = sha256:0ff902055236f70c4694c806877243e1dd52c513825a2a3ecc7eba8f5202acc8
         layer 2: digest = sha256:6b6905b8b6cc973d62fcdf70a92e8ef588196f2c5ae9da3a0551528324419683
         layer 3: digest = sha256:f89ce5ebaa0310ee79dd8ff0dea5e2c2b7664c85824ac531ba862bb40707af8f