MDEV-19942 Default installation of mariadb-server doesn't allow clients to use client plugins

while client tools technically don't need or depend on libmariadb3.so,
they need client plugins, that come with it.

debian/control

@@ -175,7 +175,7 @@ Description: MariaDB database common files (e.g. /etc/mysql/conf.d/mariadb.cnf)
 
 Package: mariadb-client-core-10.2
 Architecture: any
-Depends: mariadb-common (>= ${source:Version}),
+Depends: mariadb-common (>= ${source:Version}), libmariadb3,
          ${misc:Depends},
          ${shlibs:Depends}
 Conflicts: mariadb-client-10.0,