Add more tutorials

[traversaro]

Things to add:

• Generate/consume environment files
• Generate a Docker image out of an environment file
• Generate a Singularity image out of an environment file @GiuliaPasquale

(taken from https://github.com/dic-iit/training-conda-robotics/issues/2#issuecomment-858559452, but spin off as a separate issue as this improvements are not blocker of doing a new edition of the training)

[prashanthr05]

Some helpful material I found trying to use Docker + Conda-based development environments,

• https://github.com/KAUST-Academy
• https://github.com/KAUST-Academy/python-data-science-project
• https://towardsdatascience.com/conda-pip-and-docker-ftw-d64fe638dc45

This could be useful if you plan to add more tutorials.

[traversaro]

Thanks!