Support gitlab-ci Timestamp variables

[nolange]

Minimal .gitlab-ci.yml illustrating the issue

---
job:
  script:
    - echo "$CI_COMMIT_TIMESTAMP"
    - echo "$CI_PIPELINE_CREATED_AT"
    - echo "$CI_JOB_STARTED_AT"

Expected behavior

Output like:

2022-11-22T16:19:31+01:00
2022-11-22T16:19:32+01:00
2022-11-22T16:19:32+01:00

Host information
Debian 12 "Bookworm", x86-64
gitlab-ci-local 4.46.0

Containerd binary
podman

Additional context

Those variables are often used for reproducible builds and stored as meta-information for future reference.
Please add support for them