Resolve REANA limitations

This list includes possible limitations and other lacking features that REANA may not have in its current version. For each of the following features we wish to have, we need to firstly check whether REANA hasn't introduced it into its framework in the meantime...

- [ ] GPU support
- [ ] Workflow resource limits (There may be only limits for user in general, not for individual workflows)
- [ ] CPU limit
- [ ] Memory limit
- [ ] Disk limit
- [ ] Management of total REANA resource limits (For instance we'd expect the REANA to smartly resolve running out of reserved disk space for all workflows...)

In the past, we were able to impose resource restrictions onto workflows (or rather Docker containers) by implementing DinD (Docker in Docker) infrastructure, albeit being it rather tedious and less likely to be compatible with Kubernetes cluster.