Projects::CommitsController#show doesn't use Elasticsearch if available

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

Noted in gitaly#169 (closed)

This controller implements search functionality specifically for commits. However, it reaches into Repository#find_commits_by_message directly, instead of using a SearchService.

On GitLab EE, this means elasticsearch is never used.

Let's make the fix in CE, and have it use the appropriate SearchService instead.