allow redirects for when pages are re-named and docs/ is restructured

[dataders]

say I decided to put training.md in docs/guides/ instead of just docs/. we need a way to redirect so that links out there on the internet don't break.

Looks like Docusaurus has a plugin for this: plugin-client-redirects, and you can see how https://github.com/dbt-labs/docs.getdbt.com handles this with their _redirects file.

[dataders]

facebook/docusaurus#2843 makes me think that maybe this isn't possible w/ GitHub pages, and https://github.com/dbt-labs/docs.getdbt.com/ can only do it bc they're hosted on Netlify?