Ability to prerender outside of standard build process?

[mzealey]

Use-case: Nightly or similar updates of sitemap.xml or similar mostly-static files that need periodic updates.

Currently I have to do a whole build process in order to get any prerenders working, it would be nice to have a react-router cli addition like react-router build --prerender-only or react-router prerender which would only update the build directories prerendered files without anything else being compiled/built.