Add a topic correlation visualization

[benhammondmusic]

@eriwarr
Rather than only allowing our users to enter our compare mode and see side by side charts for two health topics, we should be able to plot the correlation (or lack thereof) on a single visualization, perhaps at the top of our compare mode view. This could be a heat map of the ratio between rates of two topics, or a scatter plot where each point was representing a state/county and the y-axis was one topic rate and the x-axis was another topic rate

EXAMPLE SITE DOING THIS:
https://cookcountyhealthatlas.org/scatterplot?layer=place&x=JG8NWHW&y=JG8CUIV&z=POP&period=2020&population=&regressed=false

Note: the user can click "verify" and it runs a linear regression, displays the trend line and reports back how significant the correlation is