insights: create a list of what aggregations are available based on a possible search query

Created by: chwarwick

It will be necessary to know what aggregations should be possible to group on based on the search that is being executed. Review the potential search keywords and document what aggregations should be possible.

type: and select: are the two that immediately come to mind that would change what aggregations are possible.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin