Log how long it takes to download cache/restore artifacts

Description

When Gitlab downloads caches or artifacts, you don't get any information about how long it took to download. I propose Gitlab displays in the UI the amount of time it took to download caches or artifacts.

In general I'd like to know how long each step of my build took, but generally I can add the instrumentation myself for the hand-written steps, so it's less urgent for Gitlab to add it than for the ones I have no control over.

Overview

What is it? When downloading caches or artifacts, print out how long it took Gitlab to download the data.

Why should someone use this feature? It's helpful to know whether large caches are slowing down your build, and what percent of the time spent on your build was spent downloading a cache.

What is the underlying (business) problem? Slow builds are expensive in terms of developer time.

How do you use this feature? I'd use it to make a decision about whether it would be good to add more things to the cache or fewer things to the cache.