Add --upgrade-and-quit or similar for unattended multi-version upgrades

(Note: this feature was added to 5.2.x and to 6.0.0, so we have two sets of release notes depicted below. The 5.2.x notes should go on the 5.2.x branch, and then we'll merge them up to master (or 6.0.x), and then the 6.0 notes should be added to master (or 6.0.x).) *** For 6.0.0 *** - A `help` subcommand has been added to display usage information to standard output. - If an invalid command is specified, usage information will now be printed to standard error, not standard output. *** For 5.2.x *** [versioning]: ./versioning_policy.html#upgrades [multiple-major-upgrades]: ./upgrade.html#upgrading-across-multiple-major-versions ## 5.2.? ### New features - An `upgrade` subcommand has been added that should be useful for cases where you want to upgrade across multiple major versions without skipping major versions (as per the [versioning policy][versioning]). See [these notes [multiple-major-upgrades] for additional information. ([ PDB-3993 ]( https://tickets.puppetlabs.com/browse/PDB-3993) )