Test on s390x and ppc64le using Canonical-hosted runners

[fnordahl]

There is an issue of the concierge snap missing architecture support for ppc64el and s390x, which makes setting up our multi architecture CI workflow more complicated.

Launchpad can build, and there are Canonical hosted GitHub runners ready to test, for these architectures. Please consider supporting them!

[benhoyt]

This seems like a reasonable request. We'll put it on our to-do list!

[carlcsaposs-canonical]

+1; s390x is part of our roadmap (https://warthogs.atlassian.net/browse/DPE-7054) —we've moved to using go install for now to unblock integration tests on s390x

am I missing something or would #81 be all that's needed?

[benhoyt]

I'm also adding ppc64le in #82. However, these PRs don't update CI to run on those new architectures, so I'll leave this issue open to test on those architectures (on Canonical-hosted GitHub runners).