The issue introduces a new migration script to have a single save object file.

From README:

The inliner takes all "by reference" visualizations in a given directory, uses the provided running Kibana instance to migrate them to the latest version, migrates the dashboard saved object as well, then transforms the by-reference visualizations into by-value panels, deletes the visualization json files and updates the dashboard json files.

The goal of this issue is to test its behavior in terms of correctness and usefulness.