Capture author and created_at data for Version

What does this MR do?

!17316 (merged) introduced new user_id and created_at columns for Versions and !18506 (merged) renamed the user_id column to author_id.

This MR introduces the setting of author_id when new versions are created.

It also contains a post-migration to backfill author_id and created_at data for Versions by sourcing from Commits. See !17322 (comment 238723580) for more information about this migration.

This replaces the previous method of sourcing Version#author data through a request to Gitaly with supplying the data through PostgreSQL.

• #13362 (closed)
• #32081 (closed)
• #13426 (closed)

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.
• [-] [Tested in all supported browsers](https://docs.gitlab.com/ee/install/requirements.html#supported-web-browsers