[ZD-13666] $JENKINS_HOME/workspace/ should not be backed up as part of system configuration (or anything else).
[ZD-13666] Correcting fix to take into account distinction between subdirectories and files.
Pointless to archive the plugins/ dir but no files in it!
Ignore $JENKINS_HOME/updates/ which is generally just downloaded stuff.
[ZD-13039] Forgot help file for ToolInstallerCachesSubject.