Avoid Gitaly N+1 in Elasticsearch commit results

What does this MR do?

In https://gitlab.com/gitlab-org/gitlab-ee/issues/9927#note_144844558 we saw that our Elasticsearch results for Commits take a particularly large amount of time to render. We already have most of the important commit information inside Elasticsearch, so let's show that information instead of asking Gitaly to load the commits from disk

What are the relevant issue numbers?

Related to #9927 (closed)

Closes #3454 (closed)

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/2016

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/2282

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer

Closes #3454 (closed)