New option: skipArtifactUpdating

[rarkins]

Describe the proposed change(s).

Add new config option skipArtifactUpdating which defaults to false. If it's set to true then artifacts updating should be skipped, regardless of package manager.

For some managers, artifact updating is done per-branch, and for others it's per-update. Where possible, it should be possible to support this new feature per-update, e.g. check update.disableArtifactUpdating and not branch.disableArtifactUpdating, and filter out any updates which have the value true. If all updates are skipped, artifact updating should be skipped. A debug log message should be printed any time skipping occurs.

The idea behind this is to allow users to skip/bypass Renovate's automatic artifact updating in cases where it's problematic, so that they can update artifacts via postUpgradeTasks or their own commit via CI.