Update all self-referential Release links from production URLs (#7720)

This commit replaces all production URLs in the Release page for NGINX
Ingress Controller with relative Hugo references instead. This improves
the consistency of URLs for the documentation set, and allows for Hugo
to handle broken link references.

Co-authored-by: Alan Dooley <[email protected]>
Co-authored-by: Gabor Javorszky <[email protected]>
Co-authored-by: Paul Abel <[email protected]>
Co-authored-by: Venktesh Shivam Patel <[email protected]>

Author: 5 people