Add a [OpenMaint](https://www.openmaint.org/en/home) instance using the Docker images and compose from https://github.com/itmicus/cmdbuild_docker. Reviewed-on: linux/WebHosting#14 Reviewed-by: bruhn_b <basil.bruhn@psi.ch> Co-authored-by: Konrad Bucheli <konrad.bucheli@psi.ch> Co-committed-by: Konrad Bucheli <konrad.bucheli@psi.ch>