Improve session cli
This MR fixes 3 issues:
- lemonldap-ng-sessions doesn't read "[all]" section from lemonldap-ng.ini
- lemonldap-ng-sessions was broken by !462 (merged) (#3075 (closed)): default behavior was to consider argument as cookie value, not storage value
- lemonldap-ng-sessions manpage is malformed: missing "DESCRIPTION", code formating for non code text,...