Bootstrap docker-compose dev environment

As a developer, I want a new generator that bootstraps a docker-compose environment with proper devcontainer.json file within my project.

See: https://code.visualstudio.com/docs/remote/devcontainerjson-reference

The output of the generator must contain:

• .devoncontaier folder with devcontainer.json file and docker-compose extends that adds the project-shell container as devcontainer runtime, enables remote debug and sets NUXEO_ENV=true env variable for activating hot-reload valve and so on.
• sample conf.d (mounted into /etc/nuxeo/conf.d folder) that enables/configure mongo template
• docker-compose.yml file that starts custom image + mongo
• end message should link to proper documentation page TBD.