Adds post upgrade step to renovate to update subchart tar files
General MR
Summary
See the linked issue for more details. By adding a new post upgrade directive to renovate.json, Renovate should now update the subchart tar files stored in ./chart/charts when changes to the subchart versions were made in the helm Chart.yaml file.
https://docs.renovatebot.com/modules/manager/helmv3/#subchart-archives
Linked Issue
Upgrade Notices
N/A