Use a single const for all valid arches

[upodroid]

What type of PR is this?

/kind bug

What this PR does / why we need it:

My change in #3405, didn't work fully as we are looking for a nonexistent arm image because we are using different arch constants in this repo. I created a new package that holds all the constants and replaced all the hardcoded strings.

https://storage.googleapis.com/kubernetes-jenkins/logs/ci-kubernetes-build/1743232758513143808/build-log.txt

level=info msg="Digest for gcr.io/k8s-staging-ci-images/conformance:v1.30.0-alpha.0.525_09a5049ca78502 on amd64: sha256:23c85bdf39f3c7332db91c80bae3f269ea831da52c0bd27c7c0bcc0fe4864fde"
level=info msg="Checking image digest for conformance on arm architecture"
level=info msg="The following error(s) occurred while looking for a build: [could not find the image digest for gcr.io/k8s-staging-ci-images/conformance:v1.30.0-alpha.0.525_09a5049ca78502 on arm]"
level=info msg="Proceeding with a new build..."

Which issue(s) this PR fixes:

Special notes for your reviewer:

/cc @xmudrii @cpanato

Does this PR introduce a user-facing change?

NONE

[xmudrii]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: upodroid, xmudrii

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