SpringBoot Add redirects for older HELP.md files

See https://github.com/spring-io/start.spring.io/issues/1529. We should add redirects so older files work.

Comment From: philwebb

Also https://github.com/spring-io/start.spring.io/issues/1627

Comment From: philwebb

Looking again, I don't think we should have redirects for 3.3.x docs. Links to the 3.2.x (and earlier) versions do redirect correctly.