advise: add an infrastructure for formatting Bash compound statements
    
    A series of context managers simplify formatting of common compound
    statements such as `if`, `else if`, `else` blocks.
    
    https://pagure.io/freeipa/issue/7036
    
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>