Allow opening files from gitui from within the parent process rather than spawning a new one with vim

[piersolenski]

A common work flow is to use gitui from within vim, using via a floating terminal window, or dedicated plugin, such as https://github.com/is0n/fm-nvim.

When opening files from within gitui, it would be great if it could use the parent instance of vim could be used, rather than spawning a new instance of vim within the window.

This is something lazygit supports via the nvim-remote setting, so it would be awesome to have feature parity.

kdheepak/lazygit.nvim#22

[extrawurst]

so its basically about adding a configuration of what program is spawned when triggering an edit?