Document how admins can retain the original behavior of the config mechanism.

Detail how admin can restore the previous behavior through the config mechanism that we introduce in 1.6 so that it’s not overwritten in upgrades.

Slack conversation: https://coreos.slack.com/archives/CG5GV6CJD/p1622709131248800

1.5: behaves like 1.4 when it comes to setting HOME/WORKDIR on tasks. In release notes we give a heads up that the default behaviour will change in 1.6 and admin will be able to configure the operator to change the default behaviour to how it was before
> 1.6: HOME/WORKDIR behavior changes and are not set by default. In docs we detail how admin can restore the previous behavior through the config mechanism that we introduce in 1.6 so that it’s not overwritten in upgrades {quote}