Corrects the way jobs are disabled for multi-stage builds to ensure all
jobs needed get run correctly.

Disables release-it from running in the multi-stage child build
pipelines, the release-it job should run in the parent pipeline only.

Closes #54

Add a template intended for standalone Python packages. The template
supports building tarballs and wheels via either setuptools or poetry,
running parallel tests via tox for multiple Python versions and
uploading packages to the GitLab package registry and/or the PyPI.

See auto-devops/python.md for fuller documentation.

This also introduces a "common" pipeline template for Auto DevOps which
brings in all of the "safe" templates. "Safe" in this instance means:

- They are only enabled if files in the repository indicate they are
  required or if appropriate variables are set.
- They can be disabled by setting a variable if they are inappropriate
  for a given project.

The Python and pre-commit templates are "safe" in that definition and so
they are added. There was a degree of duplication of the "rules:"
portions of those jobs and so they have been broken out into a common
include file.

We can use the logan tool as an example of these pipeline templates in
use. We have the following trivial `.gitlab-ci.yml` file:

```yaml
include:
  - project: 'uis/devops/continuous-delivery/ci-templates'
    file: '/auto-devops/common-pipeline.yml'
```

An example of a *push* pipeline when there *is* an open MR is at
https://gitlab.developers.cam.ac.uk/uis/devops/tools/logan/-/pipelines/350198.

An example of a *merge request* pipeline is at
https://gitlab.developers.cam.ac.uk/uis/devops/tools/logan/-/pipelines/350199.

An example of a *push* pipeline when there was no corresponding MR is at
https://gitlab.developers.cam.ac.uk/uis/devops/tools/logan/-/pipelines/350200.
Note that this pipeline runs the packaging and tox tests.

An example of a *tag* pipeline when the tag matches the package version
is at
https://gitlab.developers.cam.ac.uk/uis/devops/tools/logan/-/pipelines/350201.

An example of a *tag* pipeline when the tag *does not* match the package
version is at
https://gitlab.developers.cam.ac.uk/uis/devops/tools/logan/-/pipelines/350206.
Note that this pipeline is intended to fail and thereby *not* attempt to
publish the package.