* website: migrate to new nav-data format
* website: clean up unused intro content
* website: remove deprecated sidebar_title from frontmatter
* website: add react-content to fix global style import issue
This allows setting ForceWithoutCrossSigning when reconfiguring the CA
for any provider, in order to forcibly move to a new root in cases where
the old provider isn't reachable or able to cross-sign for whatever
reason.
