Enable Pages on Sidekiq when used

What does this MR do?

This change adds configuration for GitLab Pages in Sidekiq, resolving an issue where Pages deployments could be misconfigured because Pages was enabled on rails, but not inside the sidekiq jobs (gitlab#526022 (closed), gitlab#572552 (closed))

Related issues

Related GET issue: #1191 (closed)

Downstream issues: gitlab#526022 (closed), gitlab#572552 (closed)

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gitlab-org/software-delivery/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up-to-date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected across all expected permutations.
  • Check that the changes work across upgrades.
  • Documentation created/updated in the same MR if applicable