Write on-the-fly docker image for MS SQL

This would be experimental since it is not yet support by Nuxeo but this is the only version able to run in a docker container and on a non-Windows environment.

The image would extend the one available here:
https://hub.docker.com/r/microsoft/mssql-server-linux/

Target versions 2017, one image.

Database can be initialized through SQL.

More details on Nuxeo specifics here:
https://doc.nuxeo.com/nxdoc/microsoft-sql-server/

Target repository:
https://github.com/nuxeo/nuxeo-tools-support-priv/tree/master

Target folder:
docker/images/mssql

The DB version will then be handled in compose files through a MSSQL_VERSION variable (with a default value matching the Nuxeo version).

Add compose file for simple Nuxeo + DB scenario.