Make optional sudo chown at end of dktl.sh

[dafeder]

#9 introduces a chown command at the end of every run of the bash script that changes ownership of any root files to the current user. This addresses the common problem in docker that files created by the cli container appear to be owned by "root" to the host machine.

The solution needs to be environment-specific, as one would want to use the chown command in their local environment but not in the CI.

Acceptance criteria

• An environment variable DKTL_CHOWN is checked before running the chown command. If set to FALSE it will not run.
• The environment variable is documented.