* website: various updates

* Expose /docs and /intro views using documentation-style
layout for index pages

* Add [Use Case] Secrets Management page

* Add [Use Case] Data Encryption page

* Add [Use Case] Identity Based Access page

* Update redirects file removing `/intro` routes redirecting to
`learn.hashicorp`

* Hide MegaNav on mobile

* website: route /api straight to documentation

* Bybass index page and jump straight to content