Verified by running before and after:
mariadb --skip-column-names -e "select plugin_name, plugin_status,
plugin_type, plugin_library, plugin_license from
information_schema.all_plugins order by plugin_name, plugin_library"
Nothing else but exactly this line changed so there are no side effects:
-S3 NOT INSTALLED STORAGE ENGINE ha_s3.so GPL
+S3 ACTIVE STORAGE ENGINE ha_s3.so GPL
Also enrich config file with link to KB and unify option syntax and
standard comments.