Describe the logic of aggregation pipeline stage code ownership in the corresponding README.md or as a comment in OWNERS.yml.

The summary of the description:

• all stages have a QO and a QE class (or more in the future)
• all classes of special-purpose or special-feature stages are owned by the dedicated team
• the classes of general-purpose aggregation pipeline stages are split by the QO and the QE team accordingly

Example of dedicated teams:

• query-execution-aggregation
• query-execution-change-streams
• query-integration-analytics-extensions
• query-integration-geo
• query-integration-query-stats
• query-integration-observability
• query-integration-search
• query-integration-timeseries
• query-optimization-heuristic-rewrite
• streams-engine
• server-backup-restore
• server-catalog-and-routing
• server-cluster-scalability