Add autoscaling feature flag in release REST tests (#52096)
Add autoscaling feature flag in release REST tests (#52096)

The REST tests for autoscaling either need to be skipped in a
non-snapshot build, or alternatively, the feature flag registered so
that autoscaling can be enabled. We prefer the latter approach, as it
allows us to also test autoscaling in non-snapshot builds incrementally,
instead of at the end of development as autoscaling prepares for
release. This commit registers the autoscaling feature flag in REST
tests for non-snapshot builds.
HonzaKral/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,nknize/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,GlenRSmith/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,HonzaKral/elasticsearch