Many of the people in OWNERS no longer contribute to the project,
so clean the file and restrict to those who are still active.
Alongside this, add our core maintainers who have merge authority
on all repos.
Governance is a simple link to the Podman governance model, and
MAINTAINERS.md mirrors the new OWNERS.
Signed-off-by: Matt Heon <mheon@redhat.com>
