Add `lib/` to the Reactive image

What does this MR do and why?

This will be needed for !1112 (merged).

Expected impact & dry-runs

It doesn't seem to break the image or the service based on the jobs we run to ensure the image isn't broken and can be started.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review