Document Python packaging via the new common CI pipelie
See the individual commits for details but this MR does some tidying up of the table of contents and adds the following new features:
- Goal-oriented how-tos for Python packaging using the common CI templates.
- A new tutorial on Python packaging.
The new how-to guides can be seen at https://guidebook.devops.uis.cam.ac.uk/en/issue-198-python-packaging/howtos/.
The new tutorial can be seen at https://guidebook.devops.uis.cam.ac.uk/en/issue-198-python-packaging/tutorials/creating-a-python-package/
The new PyPI explainer can be seen at: https://guidebook.devops.uis.cam.ac.uk/en/issue-198-python-packaging/workflow/pypi/
Closes #198 (closed)