Add linux-arm64 and linux-ppc64el

[ibauersachs]

Closes #551
Closes #549

[Felixkruemel]

The CI at least fails with that error:

docker: Error response from daemon: pull access denied for libjitsi-static, repository does not exist or may require 'docker login': denied: requested access to the resource is denied.

This does not seem to be an hard issue, but I wonder why it works in 3rd CI. There it seems to be cahced which should be right as libjitsi-static is not publicly on dockerhub.

[ibauersachs]

The CI error is not directly related; I was trying to things at once (speeding up the build and adding architectures).

If you build the docker image locally to run the actual build, you'll see the vpx build error on arm. Partially at least, the image build fails too.
I have some uncomitted stuff / bash history laying around to fix the package installation (the gcc-multilib package has conflicts with an :arm64 package, there's a Ubuntu bug open somewhere).