ipa vault-archive overwrites an existing value without warning
    
    Upstream ticket was raised for issuing an warning message
    whenever data in ipa vault is overwritten.
    
    In Bugzilla(1339129) its agreed upon that Current behavior is consistent
    with other IPA commands. None of ipa mod commands asks for confirmation
    and therefore it should be the same here.
    But to document, that vault can contain only one value in ipa help vault.
    
    This PR addresses the changes agreed in Bugzilla.
    
    Resolves: https://pagure.io/freeipa/issue/5922
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>