Confusing events/second unit on rawSize metric

## Expected Behavior

In the metrics view, `rawSize` should show `bytes/second` as the unit.

## Current Behavior

`rawSize` shows `events/second` as its unit, which is misleading.

## Possible Solution

While `events/second` is an ok default unit to show for metrics of type `Meter`, custom unit names should be supported where necessary. Or an exception could be made just for `rawSize`.

## Steps to Reproduce (for bugs)

1. Go to System / Nodes
2. Click Metrics on a node with inputs
3. Search metrics for "rawSize"

## Your Environment

* Graylog Version: Graylog 6.2.0-SNAPSHOT