Refactor the automatic-crate-publishing logic, make triggered pipelines...

Refactor the automatic-crate-publishing logic, make triggered pipelines uninterruptible as well (#13908)

* Use a new approach to make automatic-crate-publishing uninterruptible

It's not neccessary to dynamically change the `interruptible` setting
for *all* jobs as the old approach does; gitlab already considers a
pipeline uninterruptible as soon as a single uninterruptible job has
started (cf https://docs.gitlab.com/ee/ci/yaml/#interruptible).

IMO this approach is more readable, as it avoids dynamically loading the
.defaults section from different files based on import conditions; the
logic is now shorter and entirely contained in the main .gitlab-ci.yml.

* Make triggered multi-project pipelines uninterruptible