[CI] Refactor pipelines on dev for greater configuration exposure and `rules` implementation

Summary

Context: !309 (comment 757309468)

At the moment, we have some pipeline configuration (such as DOMAIN_OPENSHIFT_X_Y) configured as project CI variables. This means configuration that isn't necessarily sensitive is hidden away from non-maintainers unnecessarily.

Acceptance criteria

• Non-sensitive information is specified in CI files, not in project-level CI variables
• rules are being used effectively for dev pipelines