Draft: Add systel config files for Conda

Hello,

There is some ongoing work to package openTelemac for Conda environnement (http://www.opentelemac.org/index.php/kunena/2-windows-version/14391-telemac-conda-package and https://github.com/nicogodet/telemac-mascaret-feedstock) for Windows, Linux and MacOS.

This PR add systel files for each environnement.