Update the elasticsearch image we use

What does this MR do?

Changes from elasticsearch to docker.elastic.co/elasticsearch/elasticsearch

Are there points in the code the reviewer needs to double check?

We also squeeze the memory use further, and set an upper bound on fielddata usage, to try to reduce ENOMEM errors.

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/2277