Consider making CI jobs interruptible

Gitlab CI has a feature that cancels pipelines when commits are pushed to a branch. Enabling this would save CI resource whenever a commit is pushed to a branch before the pipeline for the previous commit has finished.

See https://docs.gitlab.com/ee/ci/yaml/#interruptible. I would suggest setting a global default in .gitlab-ci.yaml

default:
  interruptible: true

Then setting it false on deployment jobs. A project-level setting also has to be enabled (see link).

Perhaps this has already been considered and ruled out? If so let's document that in .gitlab-ci.yaml