nvim: Start formatter on insertion mode

In addition to just before writing a buffer, we load the formatter
plugin when entering insertion mode.

nvim/.config/nvim/lua/plugins/formatting.lua

@@ -82,7 +82,7 @@ return {
 				end,
 			},
 		},
-		event = { "BufWritePre" },
+		event = { "InsertEnter", "BufWritePre" },
 		opts = {},
 	},
 }