add `ref` to all internal links

[tehlowkeywiz]

Using [Reference: Ethereum Search Terms](/ethereum/public-apis/reference/search-terms) vs using
[Reference: Ethereum Search Terms]({{< ref "/ethereum/public-apis/reference/search/search-terms" >}})

if we don't use ref, then build-time link checking isn't done
e.g. when someone renames a file, it'll go unnoticed