Support mount blocks for compatibility with docker driver

[optiz0r]

Docker driver prefers use of mount {} blocks over mounts list (and which is better than volumes), but podman driver fails to run with this configuration, with error:

* failed to parse config: * Invalid label: No argument or block type is named "mount".

Example snippet of job spec for a docker registry

        task "registry" {
            driver = "podman"

            config {
                image = "registry:latest"
                ports = ["http"]
                mount {
                    type = "bind"
                    source = "/data/docker/registry/data"
                    target = "/var/lib/registry"
                }
                
                mount {
                    type = "bind"
                    source = "/data/docker/registry/auth"
                    target = "/auth"
                }
            }
        }

Edit: I just realised podman does not support the mounts list either, only volumes. It is lacking the entire volume mounting capability