Respect the user commit email in more places

What does this MR do?

Uses the correct email address when performing a range of git operations via the web UI.

The user commit email was introduced in %11.4 in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21598 , but we're not currently respecting it everywhere we should. This MR fixes a number of sites.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

What are the relevant issue numbers?

Closes #51564 (closed)