[O11y][HAProxy] Revisit HAProxy `Traffic volume [Metrics HAProxy]` panel from `[Metrics HAProxy] Frontend` dashboard

[rajvi-patel-22]

Description

The Traffic volume [Metrics HAProxy] panel from [Metrics HAProxy] Frontend dashboard shows negative values due to differences/derivatives aggregation. Update panel title which describes the use case of the panel.

Screenshot

[rajvi-patel-22]

I have checked that the aggregation that was used was incorrect and is fixed in this PR, also the field is counter hence this visualization will never show negative values, so this issue can be closed now.