bug#54197: 404 link to Debuggs User Guide

[Roman Riabenko]

GNU Guix documentation at 17.7.2 Debuggs User Interfaces (16.7 for
1.3.0 documentation) links to Debuggs User Guide (in the last line
before footnotes). When accessed with info, the link is to the package
documentation, so, apparently, I cannot access it without debuggs
installed, which is expected behaviour. However, the online
documentation attempts to provide a link to the online resource, which
lands on 404. The relevant guix manual pages which need to be corrected
(in the stable and the latest manuals respectively):
https://guix.gnu.org/en/manual/en/html_node/Tracking-Bugs-and-Patches.html#Tracking-Bugs-and-Patches
https://guix.gnu.org/en/manual/devel/en/html_node/Debbugs-User-Interfaces.html
The broken link that they contain at the moment:
https://guix.gnu.org/en/manual/devel/en/debbugs-ug/index.html#Top
I assume that the link should be instead:
https://elpa.gnu.org/packages/doc/debbugs-ug.html

Roman