Support for extended tracing

[ymartin59]

I am using the following framework to design complex pipelines https://to-be-continuous.gitlab.io/doc/ and it is often required to enable tracing when developing because of large volume of shell functions.

To do so, I set following variables with expected effect in GitLab CI job log (set -x in bash typically):

variables:
  CI_DEBUG_TRACE: "true"
  TRACE: "true"

Sadly, gitlab-ci-local does not generate more output when these options.

Would it be possible to add support for these variables to implement tracing behavior?