differentiate excluded and exclude in progress process/instance in 'status json'

The moment exclude is issued on the process/instance, 'status json' shows the process/instance in the excluded field, even though
the process/instance may still be participating in the cluster and data-movement is still ongoing.

It would be nice if we could have two lists in 'status json'
- 'excluded' which are fully excluded- the process/instance does not participate in the cluster
- 'exclude_in_progress' - process/instance which are still part of the cluster and the exclude is still in progress, exclude has not completed

Start by tracing the `status json` entry point and the process/instance exclude state through cluster data movement. Identify where completed exclusion is distinguished from exclusion still in progress, then verify the JSON exposes separate `excluded` and `exclude_in_progress` lists with correct membership during both states.

Written by the indexing model from the issue text.