[TASK] Upgrade Documentation: add footer links

Add related links for each upgrade documentation file at the
end:
- link to forge issue
- link to rendered rST document

This makes it possible to
- read the documentation as rendered html with on click
- easily share an upgrade document with others
- open the related forge issue

Resolves: #90923
Releases: master, 9.5
Change-Id: Iedf874e31b7026a55275d6073d645e875dab1b6c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64044


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Siepmann <coding@daniel-siepmann.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Daniel Siepmann <coding@daniel-siepmann.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>