support AArch64 (ARM) architecture (for agents)

[tbugfinder]

Is your feature request related to a problem? Please describe.
Hardware on top of ARM architecture is getting more common in cloud and also e.g. Macs. Cloud cost efficiency is a driver too.
OCP4 is preparing for ARM architecture support.

Describe the solution you'd like
As a starting point jenkins-agents should be prepared for (intel+arm) multi-architecture builds and not only for intel/amd64 architecture.

Describe alternatives you've considered
Just use Intel.

Additional context
Multi-architecture builds might also be a good learning for the team.

[1] ocp-on-arm issues: https://github.com/openshift/ocp-on-arm/issues

[michaelsauter]

BTW, we already made some progress with this on ODS Pipeline: https://github.com/opendevstack/ods-pipeline/issues?q=arm64. Maybe some of these issues / PRs can give some helpful hints ...