Allow alternative keybindings

[akaihola]

Is your feature request related to a problem? Please describe.
My Magit muscle memory and ergonomic awareness tell me to use n/p/c-n/n-p for up/down navigation instead of reaching for arrow keys whenever I'm alternating between typing and navigating.

Describe the solution you'd like
Allow each action to have multiple keybindings.

Example:

        prevItem: [ <up>, <c-p> ]
        nextItem: [ <down>, <c-n> ]

Describe alternatives you've considered

• give up arrow keys
  • (but I often alternate between Emacs and arrow cursor navigation)
• just use arrow keys
  • (but it's un-ergonomic)
• look for a terminal app wrapper which can remap keys for just one app
  • (but it would be a hack, and I also need this for both Linux and Windows)
• look for an alternative to lazygit
  • (but lazygit is great and I haven't found a better one – Magit is prohibitively slow on Windows, gitui lacks some features)