Update GitLab Shell to v9.0.0

What does this MR do?

The main change is that the hooks are now in Gitaly, rather than gitlab-shell. Some Golang implementations of gitlab-shell functionality are also complete. Full list of changes: gitlab-shell!293 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

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