Expose job tags from .gitlab-ci.yml as predefined variable

Proposal

Currently, GitLab CI/CD provides the $CI_RUNNER_TAGS predefined variable which contains the tags assigned to the runner executing a job.

However, there is no way to access the tags that are explicitly defined in the .gitlab-ci.yml file for a specific job.

This feature request proposes adding a new predefined variable (e.g., $CI_JOB_TAGS) that would contain the tags specified in the job definition within the CI/CD YAML configuration.

This was requested by one of our customers where they need to monitor the tag usage based on the job.

Example:

We have a runner that has the tags [docker, production]

deploy:
  tags:
    - docker
  script:
    - echo "Job tags: $CI_JOB_TAGS" # shows "docker"
    - echo "Runner tags: $CI_RUNNER_TAGS" # shows "docker, production"