This adds the Zuul playbooks and role to build manylinux wheels for
aarch64 and x86_64 (while aarch64 is the primary goal; it's good for
the overall code to keep it flexible).
It first builds an sdist from the checkout and then builds the wheels
in the appropriate containers.
Note this adds the jobs in the gate pipeline, which currently responds
to Pull Requests, and the release pipeline, which responds to pushes
to refs/tags/.* (see [1]). Note for results of jobs run against tags
you will need to find the job directly from
https://zuul.opendev.org/t/pyca/builds
because there is nowhere to report the results as such (it could be
configured to send an email).
The wheels are published to the wheelhouse/ directory in the Zuul
logs, which is also listed as an artifact on the build results page.
[1] https://review.opendev.org/748323