docs: update grass-stable URL to grass-devel

[neteler]

Update manual URLS from grass-stable -> grass-devel.

Addresses #5162 (partially)

[neteler]

It was a ag and sed one-liner, should be easy.

What I did:

ag --markdown "grass.osgeo.org/grass-stable" -l | xargs sed -i 's+osgeo.org/grass-stable+osgeo.org/grass-devel+g'

[wenzeslaus]

Wouldn't be better to have the "stable" URLs everywhere regardless of a version and then change them during the doc build if needed, e.g., by adding that one-liner to the CI doc build? That way, the source code can be the same on all branches.

[neteler]

@wenzeslaus would that be somewhere here? https://github.com/OSGeo/grass/blob/4c1e37ee4db92fd3ae7ffcac1bdde6bc234f2a35/.github/workflows/documentation.yml#L186