Reverse apply stash

**Is your feature request related to a problem? Please describe.**
I have some changes for development/debugging stashed and with `git stash show -p | git apply --reverse` I can "unapply" the stash before staging to save myself some effort.

**Describe the solution you'd like**
I would like the option to reverse apply any stash from Lazygit.

**Custom Command**
```
- key: ''
context: 'stash'
command: 'git stash show {{.SelectedStashEntry.Index}} -p | git apply --reverse'
description: "Reverse apply"
subprocess: true
```