Improve result snippet text

Follow-up from #123 (closed)

Some of the result snippets are very short. They're not very helpful. How can we improve these?

Example: https://new.docs.gitlab.com/review-mr-201/search/?q=git&size=n_10_n

Some ideas of specific things we could try to address:

• Can it return more complete sentences instead of just the end of a sentence? (e.g, "Though a version of Git is supplied by macOS, you should install the latest version of Git." instead of just "version of Git.")
  • Breaking on sentence instead of phrase, maybe? https://www.elastic.co/guide/en/elasticsearch/reference/current/highlighting.html#highlighting-settings
• Or maybe it could use an ellipsis between sentences/snippets it combines. What if we showed more of the snippets, but put an ellipsis between them?
• Sometimes Google shows the meta description for a page when it's relevant. Most of our top-level/higher-traffic pages have description tags, could we use these when they're not just the boilerplate one?