Handle SIGTERM for dependent helm processes

[jonnylangefeld]

helm handles SIGTERM gracefully.
helmfile captures SIGTERM, but does nothing to pass the SIGTERM on to the helm processes to roll back those charts.
This is often painful in CI when many charts get stuck due to a SIGTERM and an immediate shutdown of the agent, once the helmfile process exited. At this time the helm processes might still be working and get killed by the agent, which leaves the chart in the "pending-install" state, from which one can only manually recover.

helmfile should pass the SIGTERM to the child processes and only exit once all child processes exited.

[yxxhero]

@jonnylangefeld please use v0.148.1

[yxxhero]

https://github.com/helmfile/helmfile