I'm not sure why, but the build fails with an obscure message. For
future reference, th build error is "could not resolve digest for
registry.access.redhat.com/ubi7/ubi:latest" and in the dockerd log the
error is "transport: Error while dialing only one connection allowed".

The manylinux image is building Python in a way that doesn't allow
linking to libpython. That's reasonable for most cases, but Pyinstaller
needs to bundle it for creating a single executable. Instead go for the
base image and use the OS packaged Python.

Pretty much the same as the python3 image but based on the manylinux2014
image. The point is when building wheel (or binaries with Pyinstaller)
it would be pretty portable to older distros.

The templates were changed and this reflects the changes:
- No need to set the order of the stages, pre-commit runs  in .pre now.
- Rename the Docker jobs for clarity and avoiding more common names.

- Update hooks.
- Add hook to validate .gitlab-ci.yml.

Because there are now scheduled CI runs.

Replace cgit with GitLab.