New recipe: dired-imenu

`dired-imenu` integrates `imenu` in `dired` so you can easily jump to
any file and directory in the current buffer (to rename it, change its
permissions...)

- Association with the package: maintainer
- Link to the package repository: https://github.com/DamienCassou/dired-imenu
- Test that the package builds properly via make recipes: done
- Test that the package installs properly via package-install-file: done