Follow up: Upgrade Elasticsearch in CI and Docker to 7.17.0

We recently upgraded Elasticsearch on GitLab.com to version 7.15.1 but that version was not available in Dockerhub at the time. The CI pipeline and Docker currently use 7.14.2 but should be updated once the image is available on Dockerhub.

Note: Elastic has their own registry where 7.15.1 is available but we've had problems with being rate limited from this registry before gitlab!21750 (merged) so we chose to go with 7.14.2 until it's published in Dockerhub.