Add a caching overlay on all docker compose images when in ci

[dannystaple]

There's a docker compose ci overlay.
Ensure the caching strategy applies to all images in the group, this should reduce the time it takes to run the github workflows.

This might be most extreme in the staging test where many minute are spent retrieving and setting up dependencies, for a test that takes seconds to run.

• Extend docker-compose.ci.yml to add caching for all services in docker-compose.yml/
• Use the overlay for all docker compose operations in .github/workflows/on_call_staging_test.yaml.

Acceptance criteria

• All workflows still pass/
• Reruns show evidence of the cache being engaged.
• .editorconfig conventions followed.