feat: Cache git repos and/or helm charts

[arkaitzj]

While using helm-git in a manifest generation pipeline I have noticed a lot of redundant git fetches, helm indexes and helm packages.

With this PR, currently using it, 2 new behaviours become available.

• Cache git repos, by setting HELM_GIT_REPO_CACHE env to an existing folder it ensures repos are only fetched once per ref, it can also be used for offline generation by copying the cache as an artifact
• Cache helm charts, by setting HELM_GIT_CHART_CACHE env to an existing folder it ensures charts are only generated once, this speeds up manifest generating pipelines by a lot if git provided charts are reused in many places.

Even just rm -rf caches && ./generate_manifests is orders of magnitude faster for us when enabling both caches

[aslafy-z]

🎉 This PR is included in version 0.14.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[aslafy-z]

Thank you @arkaitzj for this awesome addition! Looking forward to review your next contributions 💯

[arkaitzj]

my pleasure! thanks for speedy iterations! :)