Make pipeline and pipeline rule throughput statistics toggleable

## What?
Per https://github.com/Graylog2/graylog2-server/issues/12498 we implemented a toggle to enable index page stats if desired by the user. A similar toggle should be implemented for pipelines and their rules.

## Why?

General reduction of frequent API calls to the back end for information that may or may not be particularly impactful for the situation, such as when attempting to load the pipelines or rules page to disable an errant pipeline or rule impacting processing.