HAProxy visualizations using wrong aggregations

The following charts in the HAProxy visualizations are using `avg` with `derivative`:

- Connections per server [Metricbeat HAProxy] ECS
- Downtime seconds [Metricbeat HAProxy] ECS

We should _ONLY_ use `max` with `derivative` from metrics in Metricbeat and that should only be used with monotonically increasing numbers (counters). If we are trying to create a rate with a count (like `doc_count`) then we should use a `cumlative_sum` then `derivative` to scale it back to a per second interval. Also, any time we use `derivative` with a monotonically increasing number (counter) we should be using `positive_only` to handle the integer resets.

If the goal of these visualization is to display that the average is increasing or decreasing then `avg` and `derivative` will indicate that. Please confirm the purpose of these visualizations are before changing them.