In #23720 we removed the 1.7.x and 1.6.x release branches from the "active"
versions for backports. But we forgot that we needed these backports to remain
active for documentation backports because of versioned docs.
As of Nomad 1.8.0 LTS we're no longer backporting changes to Nomad CE versions
1.7.x and 1.6.x. We never got around to removing the flags in the file the
backport assistant uses to control automated backports.
Configuration changes to use backport assistant with LTS support. These include:
* adding a manifest file for active releases
* adding configuration to send backport to ENT repo
