Kubernetes overview: Operate cluster data on the frontend

What this post added

Introduced the GitLab agent for Kubernetes (agentk and KAS) to provide a secure bidirectional connection for frontend access to cluster data. Implemented user access rights for secure frontend-to-cluster communication. Developed the `@gitlab/cluster-client` JavaScript library for frontend integration. Enhanced real-time updates with the Watch API and evolved to WebSocket aggregation for improved reliability and reduced overhead when monitoring Kubernetes resources.