Allow skipping multiarch builder on PRs

[Molter73]

Description

Multiarch builders take a really long time to build, so on PRs we should allow the skip-multiarch-builds label to skip them the same way we do for collector slim and full.

Checklist

• Investigated and inspected CI test results

Testing Performed

• Run with skip-multiarch-builds retags the amd64 image. CI run
• Run without skip-multiarch-builds creates the multiarch manifest. CI run

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[github-actions]

Kernel	Method	Without Collector Time (secs)	With Collector Time (secs)	Baseline median (secs)	Collector median (secs)	PValue