Support Environment Modules as module tool

Environment Modules is in the wild and may be used by some sites as module tool. At least at CEA we use it and having support for it in EESSI will help us in the framework of the EuroHPC Federation Platform to deploy EESSI on the future Alice Recoque system.

An analysis is provided by the Environment Modules project to determine how the EESSI framework can be adapted to support the Environment Modules tool alongside the existing Lmod support:

https://modules.readthedocs.io/en/latest/design/eessi.html

I will be glad to assist with this development.