Improve unused indexes report: index definition (to support UNDO steps), better stats age (use uptime if stats_reset is NULL) , and misc. minor improvements (!64) · Merge requests · PostgresAI / postgres_ai

Added index_definition metric and added uptime time of the db as a backup in case stats weren't reset

Related issue: #48

Improve unused indexes report: index definition (to support UNDO steps), better stats age (use uptime if stats_reset is NULL) , and misc. minor improvements