Support slave links

[elbandi]

Ubuntu update-alternatives support slave links for commands items, like:

        update-alternatives \
          --install /usr/sbin/ip6tables ip6tables /usr/sbin/ip6tables-legacy 10 \
          --slave /usr/sbin/ip6tables-restore ip6tables-restore /usr/sbin/ip6tables-legacy-restore \
          --slave /usr/sbin/ip6tables-save ip6tables-save /usr/sbin/ip6tables-legacy-save

it would be nice if alternative_entry support this too.

[fraenki]

RHEL-based systems also utilize slave links nowadays:

$ alternatives --display python3
python3 - status is auto.
 link currently points to /usr/bin/python3.9
/usr/bin/python3.9 - priority 3900
 slave easy_install-3: /usr/bin/easy_install-3.9
 slave pip-3: /usr/bin/pip-3.9
 slave pip3: /usr/bin/pip3.9
 slave pydoc-3: /usr/bin/pydoc3.9
 slave pydoc3: /usr/bin/pydoc3.9
 slave python3-config: /usr/bin/python3.9-config
 slave wheel-3: /usr/bin/wheel-3.9
 slave python3-man: /usr/share/man/man1/python3.9.1.gz
Current `best' version is /usr/bin/python3.9.

Would be great to be able to manage these entries with this module. :blush: