artifacts:reports:dotenv is under documented

Problem to solve

As noted at:

#22638 (comment 404042239)

the documentation for artifacts:reports:dotenv found here:

https://docs.gitlab.com/ee/ci/pipelines/job_artifacts.html#artifactsreportsdotenv

needs to be expanded to mention that the variables are passed to dependent jobs, assuming that is deliberate behaviour that users can rely on.

Proposal

Expand the text to say something along the lines of "any variables set are also automatically accessible to any latest jobs in the pipeline that depend on the job with the artifact, as per the normal rules for when artifacts are passed to a job".