Add some .ignore entries (#18296)

Exclude node_modules and minified files from search tools like `rg` and `ag`.

.ignore

@@ -1,5 +1,8 @@
-/vendor
-/public/vendor/plugins
+*.min.css
+*.min.js
 /modules/options/bindata.go
 /modules/public/bindata.go
 /modules/templates/bindata.go
+/public/vendor/plugins
+/vendor
+node_modules