Issue 50199 - Disable perl by default
Setting PERL_ON=0 in 389-ds-base.spec.in still builds with Perl
due to the fix in PR #50200.
Introduce use_legacy in SPEC file (dropping use_perl for clarity), and
keep logic for *perl* flags in other layers for compatibility and
add *legacy* flags to encapsulate the additional changes that need to
be done to which files are being installed when building with/without Perl.
Author: Matus Honek <firstname.lastname@example.org>
Review by: mreynolds, firstyear, vashirov (thanks!)