SELinux with docker needs :Z volume mount option

[ehaupt]

When using SELinux with docker, volumes should be mounted with the :Z mount option.

This is set here:

digdag/digdag-standards/src/main/java/io/digdag/standards/command/DockerCommandExecutor.java

Lines 115 to 116 in 07c1178

	command.add("-v").add(String.format(ENGLISH,
	"%s:%s:rw", projectPath, projectPath)); // use projectPath to keep pb.directory() valid

When using SELinux, this should be:

            command.add("-v").add(String.format(ENGLISH,
                        "%s:%s:rw,Z", projectPath, projectPath));  // use projectPath to keep pb.directory() valid

Maybe a config option could be introduced:

_export:
  docker:
    image: "python:3.8-slim"
    pull_always: true
    selinux: true