Update schema with `datetime_with_timezone` type

What does this MR do?

Commits a schema change.

Why was this MR needed?

Schema generation for datetime_with_timezone was not updated during https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11229. This was fixed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12292.

In the meantime, add_timestamps_with_timezone was used without the fix.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together