Improve memory usage of event-exporter.
- event-exporter is a single replica deployment on user nodes. It currently consumes a significant amount of memory for large clusters (e.g., 800MB for 5k node cluster, 3.5 GB for 15k node cluster).
- To improve memory usage, we no longer store any watched events in memory and we only store a limited (1 item) amount of listed events to assist with Watch.
- After the improvement, memory is < 25 MB and does not increase with the number of nodes or events (e.g., 17 MB in 100 node cluster, 19 MB in 5k node cluster, 20 MB in 15k node cluster).
- The improvement does not change CPU usage and logging completeness.