List cache download/upload in Pipelines log

The duration of downloading the cache (before the build) and of uploading it (after the build) should be listed as a separate step in the log, just like "Build setup" or my script commands.

This is useful for Maven repositories, which take around 2 minutes to upload for my builds. As the Maven build itself also prints its duration, it could be confusing for users to see that some Pipelines builds take several minutes longer than the "actual" build.

Also, one cannot currently see that a build resulted in populating the cache after it finished - you have to watch the build status while it's still running to see this. Listing these steps in the log would obviously improve this.