Current: Site > Settings > General > Custom code

Add section: Site > Settings > General > Non-page requests

So I could add

1. Pairs of request and static content:
   1. robots.txt (and add static text content)
   2. some-verification-file-name.txt (and add static text content)
   3. sitemap.xml (and add static/dynamic content)
2. Redirects
   1. request (and redirect url)

This should cover a wide range or common scenarios.