Add option to perform a drain before terminating a node

Add a option (in the nodegroup.yaml configuration file) to perform a drain before terminating an instance in a node group.

This option should be per node group, as some node groups may have jobs only vs some with services only.

Start by locating the nodegroup.yaml configuration handling and the code path that terminates an instance in a node group. Trace how node groups distinguish jobs from services and how Kubernetes node draining is invoked. Done means a per-node-group option controls whether draining occurs before termination, with behavior verified for both enabled and disabled configurations.

Written by the indexing model from the issue text.