Allow building helm dependencies when dealing with local charts

[asafhm]

Eschewed features

• This issue is not requesting templating, unstuctured edits, build-time side-effects from args or env vars, or any other eschewed feature.

What would you like to have added?

Grant the option to build a local chart's dependencies before templating it.
I.e. populating its internal charts/ directory with the .tgz files of the charts it depends on, by executing helm dependency build.

If we wish to disable this by default, we could expose this functionality through a new boolean field in the generator (e.g. buildDependencies) and let the user set it to true if they wishes.

Why is this needed?

When working with local charts, it's not uncommon to find yourself in a situation where you must rely on external charts as dependencies.
That will require you to check-in those external charts' .tgz files into your source code under charts/ directory.
That is a bad practice. Working with local charts doesn't mean you have to resort to littering your git commits with binaries just to make kustomize work with helm properly.

Can you accomplish the motivating task without this feature, and if so, how?

An external generator like: https://github.com/mgoltzsche/khelm

What other solutions have you considered?

Anything else we should know?

Although using khelm may help, the problem this issue surfaces doesn't sound too complex to fix.

Feature ownership

• I am interested in contributing this feature myself! 🎉

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