docs: use absolute links for our pages

docs: use absolute links for our pages

Since 56b2970 has proven to be a no-go for us, as it breaks existing
links, let's embrace the trailing slash and use absolute links
everywhere for our pages. This way we'll get around browser cleverly
appending the relative link to the current location (since it ends with
a slash), and given our docs/ layout is flat it's not much of a hassle
either.

Converted using this beauty:
  $ sed -ri 's/(\[.+\]\()([A-Z_]+\))/\1\/\2/g' *.md

Resolves: #32088 (again) and #32310