Implement caching of the Composer packages

Won't this need #3387117: Enable distributed caching in GitLab Runner → to be in place for it to actually cache something?

Here is my try to implement the GitLab CI cache for a module: https://git.drupalcode.org/project/commercetools/-/merge_requests/3/pipe... but seems the Drupal.org's GitLab runner config misses the configuration for the cache server URL:
https://git.drupalcode.org/project/commercetools/-/jobs/4701921

Restoring cache
Checking cache for composer-11.1.4-09bfc62449f88e9b34f39b2dd9328bbff5cb5e0a-non_protected...
No URL provided, cache will not be downloaded from shared cache server. Instead a local version of cache will be extracted. 
WARNING: Cache file does not exist                 
Failed to extract cache

Who can we ping to configure this option?

You can comment on that issue. It just hasn't been at the top of the priority tasks to do, and it didn't have much activity.

For now I'll postpone this as it really depends on the infra supporting it.