BREAKING CHANGE: rename $REQUIREMENTS_FILE as $PYTHON_REQS_FILE and $PYTHON_REQS_FILE as $PYTHON_EXTRA_REQS_FILES
default extra requirements changed from 'test-requirements.txt' to 'requirements-dev.txt'

BREAKING CHANGE: removed $PYTHON_POETRY_DISABLED with $PYTHON_BUILD_SYSTEM (see doc)

BREAKING CHANGE: doc job removed
this job has to been rewritten :
	- it is in a wrong stage
	- needs an other tool (make)
	- generated doc is not publish anywhere
	- no ability to choise doc generation tool

in to-be-continuous, there is mkdocs template which is able to generate python doc too

# Conflicts:
#	templates/gitlab-ci-python.yml

Move the packaging instruction from publish job to package job.
Conforming to
https://to-be-continuous.gitlab.io/doc/understand/#generic-pipeline-stages