Remove outdated usage of "Consul Connect" instead of Consul service mesh.
The connect subsystem in Consul provides Consul's service mesh capabilities.
However, the term "Consul Connect" should not be used as an alternative to
the name "Consul service mesh".
* 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