Add timezone support for OffPeak intervals

What does this MR do?

Adds support for timezones for OffPeak times when auto-scale mode is used. For a full reference - please read #1826 (closed).

Are there points in the code the reviewer needs to double check?

• Can we (and do we even want to) make the timezone optional here bs-gitlab/gitlab-ci-multi-runner@a77fdc18?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #1826 (closed)