Based on bug 1823104 it's clear we should have some
explicit wording in the notification reference docs
about what not to include in versioned notification
payloads, so this change attempts to start that with
the most obvious thing - don't expose access credentials
to the nova deployment.
This also adds a reminder to think about what is being
added / mirrored from internal objects and determine if
consumers really need it and if they aren't asking, opt
to not including it until requested.
Change-Id: I326aa39d963091282a5d0b70ba222abfe8ccfdac
Related-Bug: #1823104
8856009445