manual: keyword index URLs partially broken

[neteler]

Some links at are still partially broken:
https://grass.osgeo.org/grass82/manuals/keywords.html

@tmszi seems a double // leaks in somewhere, only discovered that now.

I cleaned up the local server patches, updated and recompiled.

This effect only happens with the "grass-stable" redirects:

https://grass.osgeo.org/grass-stable/manuals/addons/d.vect.colbp.html --> https://grass.osgeo.org/grass82//manuals/addons/d.vect.colbp.html

Probably it is an issue of the Apache redirect (but I think to not have seen it before).

I found // in URL here https://grass.osgeo.org/grass82//manuals/index.html

Some links also contain the grass.osgeo.org server setup related internal directory names.
Not sure if Apache redirects interfere or the local setup (see https://github.com/OSGeo/grass-addons/tree/grass8/utils/cronjobs_osgeo_lxd#web-site-organisation).

Originally posted by @tmszi in #780 (comment)

[tmszi]

Some links at are still partially broken: https://grass.osgeo.org/grass82/manuals/keywords.html

Yes you are right, core modules links still use absolute path instead of relative path, fixed with OSGeo/grass#2574.