gitlab secrets, build args are not passed to kaniko at build time by default

Kaniko does not consider any build arguments, nor secrets from gitlab by default.

Steps to reproduce:

1. clone example repo

2. add:

   ARG BUILDARG
   RUN echo I received "${BUILDARG}" from kaniko!

3. Add BUILDARG in your CI/CD settings.

Example here: https://gitlab.cern.ch/dsouthwi/build_docker_image/-/jobs/5328661

This may be fixed by modifying the build argument for kaniko with docker-style --build-arg ARG_IN_GITLAB=$GITLAB_VAR_NAME for every single argument, but is painful for builds with many arguments.

Is there a gitlab array argument that might be passed? i.e. --build-arg $CI_USER_ARGS=[for arg in $CI_USER_ARGS;do;ARG=${ARG};done;] etc?