Automatically remove flakehell dependencies from `mkdocs_template_rdeville` as
flakehell seems to be dying.
Replace flakehell by flake9, fork of flake8 with pyproject support.
Update files accordingly.

Fix pydocstyle warning in plugins.py files.

Upgrade CI from mkdocs_template_rdeville.

Add/upgrade following files using the mkdocs_template_rdeville:

- .editorconfig
- .yamllint
- mkdocs.yml
- pyproject.toml

Disable pylint error for duplicate files and remove preview folder from
pylint test.

Add following syntax and test config files :
  - pyproject.toml
  - .editorconfig
  - .yamllint