Announcing Vitess 18

Vitess 18 introduces support for Vitess-managed foreign key constraints within the same shard, enabling data import from existing MySQL databases with FKs. It also enhances general compatibility with a revamped query planner supporting complex aggregations, subqueries, and derived tables. Usability is improved with the migration of the CLI to Cobra (enabling auto-generated docs and shell completion) and the completion of the vtctldclient migration. VReplication and online DDL now support near-zero downtime migration from external databases and better progress estimates. Point-in-time recovery is now available without an external binlog server. The tablet throttler uses gRPC for communication, and the benchmarking system ('Arewefastyet') has been updated.