Use relative links instead of absolute ones on top

At this moment, even from the root of the Review Apps shown in the MR, we (specifically reviewers) will be taken from the review app to the production docs since we used the absolute URLs on top page.

This MR replaces them with relative links.

Tweaks

While we could use /ee/... here, ./ee/... is used. That would helpful when community contributor can use their own review apps on gitlab.com's Review Apps with GitLab Pages without custom domainname in their Community contribution.