Add a context menu to the Undo Commit section

### Describe the feature or problem you’d like to solve

When I want to amend a commit, I often find myself right-clicking the Undo Commit area at the bottom of the sidebar, expecting it to offer up the same menu as the commit does in the History tab.

### Proposed solution

Add a context menu to the Undo Commit area with similar options to the one in History. Specifically:

- Amend Commit…
- NOT undo commit since that is available through the button
- NOT revert commit since that could be confusing, and I’d imagine people rarely want to immediately revert
- Create Branch from Commit…
- Create Tag…
- Cherry-pick Commit…
- Copy SHA
- NOT view on GitHub since that only is enabled after pushing (and therefore after the Undo Commit section is removed)

### Additional context

N/A