Convert to use PyPI `pid` instead of `python-pidfile`

[portante]

Convert to use PyPI pid instead of python-pidfile.

It appears that an RPM exists for pid in Fedora packaging, python3-pid (at least as of Fedora 36) so we won't have to carry a pip3 install package for it.

[pravins]

We do have python-pidfile also in Fedora now, See https://koji.fedoraproject.org/koji/packageinfo?packageID=36125
Even without this fix we will get rid of pip3 install package for it :)

[portante]

While that may be true, the pid project is a year more active upstream (Nov 2020) than the pidfile project (Dec 2019, aside from @vishalvvr's recent license PR), and the pid project has more stars and forks on GitHub that the other.

[webbnh]

My concern is that we support more than just the latest version of Fedora: we support at least one older version, as well as CentOS Stream and RHEL. So, the fact that the RPM is now available for the latest Fedora isn't all that impressive if we don't have it in most of the other places that we want to go (and, that's equally true for pid and pidfile...).

[portante]

FWIW, python3-pid is already shipped with RHEL 8. I doubt we'll be able to convince RHEL to take in another package like pid that is already there.

[pravins]

Right, getting into RHEL, is very difficult, but we can get this package in epel.
Getting into Fedora 35, is also easy, just need to request that branch.

Off course, we can move pidfile to pid, this is not a big task as well.
As far as i think, its low priority now due to availability of python3-pid package.