Tripleo-upgrades-fs-variables

Tripleo upgrades releases control variables

 * They are used at tqe, tripleo-upgrade and toci
 * The the "_step" variables are only used by the legacy role "overcloud-upgrade", and this is only used by the jjb tripleo-quickstart-upgrade-baremetal-builder
 * The containerized_overcloud_upgrade and containerized_undercloud_upgrade just state if we want to go to a containerized, but from a release point of view doesn't matter.
 * The role tags are selected at toci, and they control the flow of execution in the upgrades.

Upgrades job change injection points
This table show where and when a change in review is getting injected in the job O UPGRADE currently really means "undercloud packages during overcloud upgrade" and ideally "undercloud packages and overcloud containers during overcloud upgrade" In rocky+ releases it will probably mean "undercloud containers and overcloud containers during overcloud upgrade"

(*) we already install n in undercloud so we are not really testing any upgrade in undercloud

(**) if a change is only in undercloud only repo, then we can always inject changes, but they will not be used. So it's safe to do it anyway.