MDEV-24728: Debian include client caching_sha2_password plugin

Backport of 4bc31a90

Include client libraries for auth caching_sha2_password and
sha256_password in the libmariadb3 client library package.

debian/libmariadb3.install

@@ -4,3 +4,5 @@ usr/lib/*/libmariadb.so.*
 usr/lib/mysql/plugin/dialog.so
 usr/lib/mysql/plugin/mysql_clear_password.so
 usr/lib/mysql/plugin/client_ed25519.so
+usr/lib/mysql/plugin/sha256_password.so
+usr/lib/mysql/plugin/caching_sha2_password.so