HAProxy: fix problems when upgrading from the 19.03 platform that needed manual
intervention. The stats socket line from the old example config is now
obsolete and disabled if it still appears in user config.
It can be removed after the upgrade. (#PL-129632).
Make our release channel usable for importing from a pinned version.
This is recommended in our docs but only worked for upstream NixOS channels before.
Now, packages from our overlay can be installed in custom user environments in
combination with channel pinning (#PL-129619).
Include symlinked files in local config directories for Nginx, HAproxy and
SystemD units. They were silently ignored before (#PL-129628).
Add Python3 to Sensu check environment (#PL-129656).
Gitlab: update to 13.6.6 security release (#PL-129665).