Add footer links to HIG and Contributor Guide

[zeebok]

Problem

Code docs contains handy links in the footer for getting around to the other guides, among other pages but the HIG and Contributor Guides do not contain these.

Proposal

Copy the same footer nav from Code docs into HIG and Contributor Guide

Prior Art (Optional)

No response

[danirabbit]

HIG and Contributor Guide are each their own repos

[danirabbit]

Added to HIG, moving to contributor guide

[LuminousHustler]

Marking this as blocked by elementary/website#3947. Web development is super reliant on a test environment. Running the website in a container currently doesn't work. Although this isn't directly blocked by this issue, it does make addressing it pretty tricky