Allow adding external scripts to the index.html

[Zhomart]

Currently these is no way to add more <script src="local or extern"> </script> tags. Having this is useful to add local or external swagger-ui plugins.

I'm thinking of this kind of config

	r.Get("/swagger/*", httpSwagger.Handler(
		httpSwagger.ScriptSrc("https://unpkg.com/htm@3.1.1/dist/htm.js"),
		httpSwagger.ScriptSrc("https://unpkg.com/react@17.0.2/umd/react.production.min.js"),
		httpSwagger.ScriptSrc("/static/myplugin.js"),
		httpSwagger.Plugins([]string{"MyPlugin"}),
		httpSwagger.URL("http://localhost:1323/swagger/doc.json"), //The url pointing to API definition
	))