ARM CI Build(s), master branch (2022.02.21.)

Enabled the build of a couple of the projects on ARM64 as part of the CI.

The k8s-arm tag was advertised on: https://mattermost.web.cern.ch/it-dep/channels/aarch64-arm64 Apparently it's not quite "official" yet, but I wanted to jump on it already. 😉

Note that I encountered some issues with the LCG GCC installation and Xerces-C package while playing with this MR. See: https://sft.its.cern.ch/jira/browse/SPI-2432

Pinging @elmsheus and @fwinkl.