feat: add watchexec plugin

lua/plugins/watchexec.lua

@@ -0,0 +1,8 @@
+return {
+  "StevanFreeborn/watchexec.nvim",
+  lazy = false,
+  config = function()
+    vim.api.nvim_set_hl(0, "WatchexecSuccess", { bg = "#7ec8c0" })
+    vim.api.nvim_set_hl(0, "WatchexecFailure", { bg = "#d47373" })
+  end,
+}