amend: add config option to update time to current in hg amend (issue5828) The given config option i.e. `rewrite.update-timestamp` updates date to current when //True//. However when only date is to be updated to current with the working directory clean and no other attributes changing then it does not amend as stated in issue 5828. Further when `--date` flag is specified along with the new config option then `--date` is given priority over the config option. Differential Revision: https://phab.mercurial-scm.org/D5491