multiple fixes

Context

This MR adresses issues encountered in multiple merges (mostly aidge_quantization!10 (merged))

1. Split download:....:script in multiple parts (before_script & script)

Context:

1. aidge_quantization needs aidge_onnx but only for testing
2. The stage build_cpp exists on aidge_quantization but not in aidge_onnx. Which means that when building ubuntu_cpp jobs, download:....:script was looking for artifacts of aidge_onnx/ubuntu_cpp jobs. Which led to failure since they don't exist.

What I did

Created a before_script section for download:ubuntu/windows:artifacts/repos that replaces current script section :

Hence I replaced all

!reference[ download:ubuntu/windows:artifacts/repos , script] 

with

!reference[ download:ubuntu/windows:artifacts/repos , before_script] 

Just like before, name a job and this before_script will retrieve all artifacts from dependencies listed in `download:list_dependencies`

    - DEPENDENCY_JOB="build:ubuntu_python"
    - !reference [.ubuntu:download:artifacts, before_script] 

what does the script parts does ?

1. at least 1 repo name in the form of an array (DEPS_NAMES)
2. a job name

    - DEPS_NAMES=("aidge_onnx")
    - DEPENDENCY_JOB="build:ubuntu_python"
    - !reference [.ubuntu:download:artifacts, script]

And will retrieve all specified jobs of given name in given repos.

2. Refactored rules

There was an issue with the rules with some jobs not being able to be started manually.

3. Refactored & cleaned up ubuntu python coverage & test

There were too many invocations of source venv/bin/activate which was messing the env in which test & coverage were executed.

Also adapted to the fact the in aidge_quantization!10 (merged) there is an override of the before_script of these jobs.

4. Homogeinezed the installs with of apt dependencies

now everything is retrieved through the .retrieve_deps:apt: script located in defaults.gitlab-ci.yml

Later on this

5. Fixed pip release testing script

The script was not working properly for aidge_export...