Expire artifacts in a week by default

[martijnbastiaan]

We're currently using a whopping 523.5 GiB project storage on GitLab.

Still TODO:

• [X] Write a changelog entry (see changelog/README.md)
• [X] Check copyright notices are up to date in edited files

[leonschoorl]

While it's probably good to have some sensible default. I don't think this will change anything for the current situation. Looking for artifacts configured I found:

• .gitlab-ci.yml#L84
• .ci/gitlab/benchmark.yml#L45
• .ci/gitlab/publish.yml#L11
• .ci/gitlab/test.yml#L68

All of which already have expiration defined, so those will override the default you add here I assume.

[martijnbastiaan]

Well it doesn't seem like the 500 GB is caused by this. The default expiration period of 30 days shouldn't amount to this. It's more likely that it's all the stale branches, like you both noticed. Closing!