Add query relevance timeline to event search (and general search when available)

### Feature Description

_A clear and concise description of the feature you're requesting._

The "classic" keyword relevance over time plot:

x is time / dates
y is relevance of search query

on hover of the points it shows the meeting that happened to make that query relevant
in the hover details you can click a link to the event

probably want some method for changing the x axis timeline, zoom or or scroll to change dates shown

### Use Case

_Please provide a use case to help us understand your request in context._

1. it seems fun
2. it provides another method for seeing the contextual history of a query over a council
3. it can help show people that we can do interesting things with our data model -- get them interested in the "analysis" side of CDP

CC @tohuynh