Announcing Vitess 21

Vitess 21 is now generally available, focusing on enhancing query compatibility, improving cluster management, and expanding VReplication capabilities. Key features include reference table materialization, multi-metric throttler support, enhanced online DDL functionality, a new mysqlshell engine for backup and restore processes, and detailed execution traces and schema analysis with vexplain. The Vitess Kubernetes Operator introduces horizontal auto-scaling for VTGate pods and Kubernetes 1.31 support, improving overall scalability and deployment flexibility.