[ci.jenkins.io] Enable Maven dependencies client-side caching for BOM with Job Cacher

[dduportal]

As described in #4442, the Artifact Caching Proxy (ACP) is not following up with the BOM build with their new size (> 1000 parallel stages).

ACP still makes sense infrastructure-wide to share cache between builds of ci.jenkins.io (to decrease the impact on the outbound bandwidth of our Artifactory) in a safely manner (no cache poisoning as it's only a proxy to existing system).

But an additional solution is required for the BOM to ensure:

• no slower or blocker of the BOM releases as BOM builds could fail for a few stages only due to ACP, which requires re-triggering a build each time it fails
• faster feedback loop around BOM builds (PR adding new items, releases, etc.) to catch testing issues a bit earlier
• BOM build costs stays sustainable regarding its sudden growth in the past months

As such, we want to set up a Maven client-side caching: if Maven has most of its artifacts, then it uses them. It's the same idea as any developer machine.
Of course, ACP keeps being used as the second layer of cache.

@timja did a PoC as per #4442 (comment), which can bee seen in the PR jenkinsci/bom#4351.

Task list:

• Add the jobcacher plugin to ci.jenkins.io
  • Manually (done by @timja for the PoC)
  • In Puppet's code
• Validate the PoC impact
  • Cache lifecycle (seeding between branches, cache poisining risk, etc.)
  • Impact on the ci.jenkins.io metrics
• Run the PoC on aws.ci.jenkins.io with AWS S3 bucket (or fall back to a local drive)