Add documentation for .Subcharts to the Built-In Objects documentation

[njiang747]

As of Helm 3.7, .Subcharts.<subchart_name> exposes the scope of a subchart (including .Values, .Chart, .Releases, etc.) to the parent (see helm/helm#9957).

It would be great to document this on https://helm.sh/docs/chart_template_guide/builtin_objects since it doesn't seem to be available anywhere in the documentation.

Thanks!

[EvanCarroll]

This would be great. It would be nice to know how to access dependency information of a subchart. This would allow us to receive things like their default password and credentials, rather than having to compute and set from parent.

I also didn't see any tests in the repo that have a string for .Subchart seems the functionality is very young.

[remram44]

Wow, this is exactly what I need. How can a feature exist and not be documented for a year?

What the hell does .Subcharts do exactly? Does it include .Values.global?

[remram44]

Nevermind "a year", this is the solution to a 6 year old issue (helm/helm#3920) that was implemented 3 years ago (helm/helm#9957). Yet it has been kept completely hidden.