Nephron: Test if pane accumulation has a positive effect on performance

The PaneAccumulator class can be used to accumulate panes. This can be used to reduce the number of flow summaries written to ES. It may even have a positive impact on pipeline overall performance.

The pipeline builds all other aggregations on-top of the conversation aggregation. It should be tested if inserting a pane accumulation right after the conversation aggregation increases pipeline overall performance.