* website: Update all Learn crosslinks
The URL structure on Learn recently changed, so it's time to update some URLs.
Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com>
As well as some general consolidation and reorganizing, this also includes
some updated advice for making the best use of new Terraform v0.12
features to create infrastructure building-blocks.
In particular, the "Module Usage" documentation is now consolidated into
the configuration section in order to bring all of our general language
documentation together, and the top-level "Modules" section is now
primarily focused on module _authors_ as an audience, covering topics such
as publishing modules and designing them for reuse.
Nick Fagerlund