ovpnmain.cgi: Updated fix for Bug#13137

ovpnmain.cgi: Updated fix for Bug#13137

- This now only adds "providers legacy default" to the config files of connections that
   have legacy certificates, both for n2n and roadwarrior.
- This new approach also removes the requirement to have code in the update.sh script
   or in backup.pl so those earlier modifications are removed in two additional patches
   combined with this one in a set.
- The -legacy option has been removed from the pkcs12 creation part of the code as
   otherwise this creates a certificate in legacy format, which is not wanted. All new
   connection certificates being created will be based on openssl-3.x

Fixes: Bug#13137
Suggested-by: Michael Tremer <michael.tremer@ipfire.org>
Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>