This got lost somewhere along the way (almost certainly by me), so this
commit tries to make it explicit. The app needs to be able to configure
the session cookie domain name so that it is valid for both the main
site domain and the authentication subdomain. For instance, if the site
is runnning at uat.atat.code.mil and authentication happens at
auth-uat.atat.code.mil, SESSION_COOKIE_DOMAIN should be set to
atat.code.mil so that it's valid for both.
This adds the setting to the base INI file and a default for our K8s
clusters.
60b12fca52