Add filter feature to site

[Frijol]

The External Resources page has a whole lot of Info modules with different external resources. On the backend (not currently part of the JSON but in this spreadsheet which the JSON is generated from), I've tagged each of these with e.g. "Air" "Health" topic areas.

It would be really great to create a frontend JS feature that allows users to filter the resources by these topics. Something like the dropdown filter bar from this:

(actually that gif comes from https://www.npmjs.com/package/ng-multiselect-dropdown-gp - maybe use that?)