Upgrade elasticsearch gems to v6

What does this MR do?

These were very out of date. We update to v6 versions as we are targetting v6 compatibility for now. This hopefully helps get us closer to supporting v7 as well.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Manual QA

1. Enable ES
2. Create a project with snippets, code, commits, issues, issue comments, merge request comments
3. Perform searches for all resource types using * search
4. Perform boolean search tests like a | b and (a | b) + c
5. Trigger a complete re-index using bundle exec rake gitlab:elastic:index and again try all searches
6. Start again but with only having Elasticsearch enabled for a single group and again try all searches
7. Check the elasticsearch/logs/*.log and gdk tail elasticsearch for any errors or warnings

#32539 (closed)