Clarify the installation setup

The latest PyPA guidelines recommends to use pyproject.toml instead of setup.py configuration files (PEP 621) and updated their recommendation regarding the de dependency specification (PEP 631).

These changes provide the opportunity to:

• replace the setup.py by a pyproject.toml configuration file.
• release the install_requires dependencies constrains to be less restrictive. Note: reproducible build requires a explicit requirements.txt file with the actual pinned versions (installed with --no-deps).
• isolate the the source-code folder in a src/ directory.

We will investigate the need to migrate to a poetry build setup to simplify the dependency managment.

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Additionally, we need to update the docs to highlight that no python libraries should be installed on the python system.

If the user needs to install the tool locally, it should be done in a conda/venv/mumba isolated environment:

conda create -n moon-coverage python=3.8
conda activate moon-coverage

or

python -m venv venv
source venv/bin/activate

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Typo: globally-> locally