Enable Elasticsearch on handbook pages

[goldenapples]

Recently I was searching the handbook for "behavior" and didn't see any results. This makes sense because we're just using a plain text search, and the American spelling doesn't appear anywhere in the handbook, but it surprised me.

I think it would be a nice enhancement to switch the handbook search to Elasticsearch so that we can give better fuzzy-matching results. This will be helpful in cases like this where there are regional spelling variants of words, as well as being able to search by synonyms or phrases more generally.

I'm not sure how much of a lift it would be, but if it's an easy update, we should use ES for Handbook search results.