git_ui: Show author name on commits in branch picker (#36812)

See related discussion
https://github.com/zed-industries/zed/discussions/36511.

<img alt="zed"
src="https://github.com/user-attachments/assets/da7fc30d-2504-48f4-a392-7c8d5cd8acb1"
/>

Release Notes:

- Added option to show the author name in a branch picker commit
information

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/git_ui/src/project_diff.rs

@@ -1220,6 +1220,7 @@ mod preview {
                         sha: "abc123".into(),
                         subject: "Modify stuff".into(),
                         commit_timestamp: 1710932954,
+                        author_name: "John Doe".into(),
                         has_parent: true,
                     }),
                 }