Deploy and serve coverage report web page via GitLab Pages

Currently, GitLab Pages is used to serve the auto generated Sphinx documentation.

We should find and decide for a solution to distribute the documentation and the test coverage report in parallel.

Something like:

• https://clients.pages.duniter.org/python/duniterpy/doc/index.html
• https://clients.pages.duniter.org/python/duniterpy/test/index.html

Or, even better:

• https://py.duniter.org or https://duniterpy.duniter.org
• https://clients.pages.duniter.org/python/duniterpy/index.html