Add `stash` options to staging panel

### Is your feature request related to a problem? Please describe.
This is entirely a UI quality of life feature.

When staging hunks in the staging panel, on can directly `commit` from there. However, the option to `stash` is not available in `local` bindings. To stash currently staged changes one has to exit the staging panel and into the Files panel to access `stash`.

### Describe the solution you'd like
Enable `stash` option(s) in staging panel to stash currently staged changes.

### Describe alternatives you've considered
Exiting staging panel and running `stash` from Files panel still works. Just one more step.