Signifcant performance overhead on watching .git folder

I have been debugging why in some of the folders my plugin [fff](github.com/dmtrKovalenko/fff) scan is very contended and sometimes very slow on a large git repo and as appeared the reason is this function

https://github.com/akinsho/git-conflict.nvim/blob/a1badcd070d176172940eb55d9d59029dad1c5a6/lua/git-conflict.lua#L458-L470

you are setting recursive watcher on the `.git` folder unconditionally in case of chromium monorepo the `.git` folder is **64GB and 700k+ object files inside** - this exhauses the file system watcher, adds a lot of VFS load and simply unnecessary

Instead you can watch specifically one file `.git/index` - you can watch exatly one path and keep the exact functionality untouched