Feature flag: look up commits without batch-check

What does this MR do?

Introduction of the new feature flag commit_without_batch_check that switch git object extraction process. If enabled there won't be call to 'git cat-file --batch-check' before 'git cat-file --batch' to extract the object.

Gitaly MR: gitaly!1711 (comment 274656766)

Relating to issue: gitaly#2255 (closed)

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

There is no need in testing. All checks are covered by unit test during CI process.
There should be no impact on the current state of things.