Follow-up to Elasticsearch blog post

Proposal

We had https://about.gitlab.com/2019/03/20/enabling-global-search-elasticsearch-gitlab-com/ in March. Kenny pointed out in the group conversation today that as we've learned lessons since then, and have updates to provide, it would be cool to add a new blog post with those details.

Checklist

• If you have a specific publish date in mind
  • Include it in the issue title
  • Give the issue a due date of a minimum of 2 working days prior
• If time sensitive
  • Added ~"priority" label
  • Mentioned @rebecca to give her a heads up ASAP