Add last_used column in information_schema.index_statistics

To check, if an index will ever used , a column last_used would be helpful.

Alternatives like
https://mariadb.com/kb/en/performance-schema-table_io_waits_summary_by_index_usage-table/
is only temporary and not permanent.

Column should be of type date and only be updated, if different from current day to avoid too much load.