after/ftplugin instead of autocmd

Use after/ftplugin instead of autocmds to handle options depending on
filetype

after/ftplugin/gitcommit.lua

@@ -0,0 +1,8 @@
+-- TIP: If you want custom color of colorcolumn local to window
+-- do
+--     local ns = vim.api.nvim_create_namespace('gitcommit')
+--     vim.api.nvim_set_hl(ns, 'ColorColumn', { link = '#ff0000' })
+--     vim.api.nvim_win_set_hl_ns(0, ns)
+-- end
+vim.bo.textwidth = 72
+vim.wo.colorcolumn = "+0"