Make Stream/Dashboard/Alerts search widget default to searching both title and description


## What?
When using only keywords in the search widget for Streams, Dashboards, Alerts and the like only the title is searched. Instead the search should by default search through title and description.

## Why?
Intuitively doing a search without any filter modifiers should be broader than using a specific filter. Users need to know, learn and remember to use extra syntax to also search through descriptions. They might not remember the title of something, but keywords from the description an object might have and get frustrated.

* Graylog Version: 6.0.3