Map current documentation to new structure

docs/apis/delivery-service.mdx

docs/apis/routing.mdx

docs/authentication.md

docs/event-log.mdx

docs/getting-started/account.mdx

docs/getting-started/authentication/applications.mdx

docs/getting-started/authentication/users.mdx

docs/getting-started/encryption.mdx

docs/getting-started/overview.mdx

docs/getting-started/receiving/decrypt.mdx

docs/getting-started/sending/encrypt.mdx

docs/rate-limiting.mdx

docusaurus.config.js

sidebars.js

src/components/ApiSpec.js