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/collab/migrations.sqlite/20221109000000_test_schema.sql

@@ -101,6 +101,7 @@ CREATE TABLE "worktree_repositories" (
     "scan_id" INTEGER NOT NULL,
     "is_deleted" BOOL NOT NULL,
     "current_merge_conflicts" VARCHAR,
+    "branch_summary" VARCHAR,
     PRIMARY KEY(project_id, worktree_id, work_directory_id),
     FOREIGN KEY(project_id, worktree_id) REFERENCES worktrees (project_id, id) ON DELETE CASCADE,
     FOREIGN KEY(project_id, worktree_id, work_directory_id) REFERENCES worktree_entries (project_id, worktree_id, id) ON DELETE CASCADE