Add an undo button to the git panel (#24593)

Also prep infrastructure for pushing a commit

Release Notes:

- N/A

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>
Co-authored-by: Conrad <conrad@zed.dev>
Co-authored-by: Nate Butler <iamnbutler@gmail.com>

crates/git/src/git.rs

@@ -38,6 +38,7 @@ actions!(
         StageAll,
         UnstageAll,
         RevertAll,
+        Uncommit,
         Commit,
         ClearCommitMessage
     ]