Install man pages with pixi global

[asmeurer]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

pixi global install gtop 
man gtop # doesn't work

Issue description

pixi global does not install man pages. It should be sufficient to just create ~/.pixi/share/man and install the files from the package into there. man automatically searches for share/man directories alongside the directories in PATH. For example

mkdir -p ~/.pixi/share/man/man1
conda install gtop
cp ~/miniconda3/share/man/man1/gtop.1 ~/.pixi/share/man/man1/
conda remove gtop
man gtop # works
man -d gtop # confirms that the manpage is found in ~/.pixi/share/man/man1/gtop.1

Expected behavior

manpages should be linked from the pixi global envs.