Local cache for helm charts

[yorik]

I'm trying to use flux-build for not a big gitops repo, but it downloads ~30 helm charts 4000 times! This overloads our registry and slows down rendering a lot.

I've seen that there are commented out attempts to add cache, also there are different caching in helm packages. I could contribute, but would appreciate some hints how to do it better.

Thanks!

[raffis]

This part is mostly from upstream and was disabled in this initial version. I do agree that we need a caching layer here thats why it was left commented in the code.
Happy to merge a pr regarding this! Likely to be extended in https://github.com/DoodleScheduling/flux-build/blob/master/internal/build/helm.go#L464

You might also check upstream flux source-controller base regarding that bit.