MDEV-20298 Make mariadb-client-10.5 perl dep backwards compatible

The package libdbd-mariadb-perl has been available in Debian September
2018, so it is already included since Debian Buster and Ubuntu Disco.

Use it as the primary Recommends for MariaDB client binaries, but keep
the MySQL variant as a fall-back in case this package gets backported to
older releases that did not yet have it.

This change was done in downstream Debian packaging in
https://salsa.debian.org/mariadb-team/mariadb-10.4/-/commit/bb4ad78bc10a1b52558c4c30600a02e30c4ce0a9

debian/control

@@ -365,7 +365,7 @@ Provides: default-mysql-client,
           mysql-client-5.7,
           mysql-client-8.0,
           virtual-mysql-client
-Recommends: libdbd-mariadb-perl,
+Recommends: libdbd-mariadb-perl | libdbd-mysql-perl,
             libdbi-perl,
             libterm-readkey-perl
 Description: MariaDB database client binaries