Enable Toggle of Highlighted Values in the UI

Currently, a value in a search or a widget may be highlighted, so that it shows more prominently in the UI, calling the user's attention to it. There is no way today to turn that highlighting back off if desired.
## Expected Behavior

When you highlight a value, the menu item should switch to "stop highlighting this value" and enable you to turn off highlighting for a particular value.
## Current Behavior

If you highlight a value in a search, then create an aggregation that includes that value, it will be highlighted in the aggregation as well. If you then save that aggregation as a dashboard, the highlights will carry through to the dashboard and cannot ever be disabled.
## Possible Solution

Change the menu item to be more of a "togggle switch", turning highlighting on or off as needed.
## Steps to Reproduce (for bugs)

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## Context

More an annoyance than anything, but it can lead to undesired results in the UI for customers.
## Your Environment

* Graylog Version: 4.x
* Java Version:
* Elasticsearch Version:
* MongoDB Version:
* Operating System:
* Browser version: