CI: allow "never" in job:artifacts:expire_in

Please make this possible:

job:
  artifacts:
    expire_in: never  # <----- THIS
    paths:
    - something

Currently, it's only doable via UI using "Keep" button:

CC @markpundsack @bikebilly @markglenfletcher @ayufan

Good idea :)

added auto updated potential proposal labels

Customer is interested in this (internal).

added customer label

added 1 deleted label and removed 1 deleted label

Ultimate customer interested in this feature: https://gitlab.my.salesforce.com/00161000004yxj9

changed milestone to %Backlog

I'd like this feature as it would make it easier to expose artifacts as release assets.

What do you think? @jlenny @dimitrieh

Makes sense to me. Linking to https://gitlab.com/gitlab-org/gitlab-ce/issues/56023 where we'll need to determine how to solve this.

I think this suggestion is also relevant for gitlab-ce#17081 (junit test reporting), where the reporting at the moment disappear when the artifacts are deleted (if I understand correctly).