feat(manager/kustomize): Support inflating helm charts

[micke]

Changes

1. Add support for extracting helmGlobals options from kustomization files to support custom destination for inflated helm charts.
2. Add support for inflating helmchart deptypes in the kustomize manager.

Context

Closes #14137

The helm charts will be inflated if any of the following is true:

1. The currentVersion is inflated, OR
2. The kustomizeInflateHelmCharts postUpdateOptions is enabled.

If the currentVersion is inflated then they will be deleted.

If the chart is already inflated then Renovate won't try to inflate them again.

I decided to accomplish this by directly interfacing with helm commands to inflate the charts by calling helm add instead of relying on using kustomize build to have kustomize inflate the charts.

I took this approach because i've seen setups where a kustomization might need pre-processing to be able to be built, a common example of this might be encrypted secrets, where the secrets referenced in the kustomization need to be decrypted before using kustomize build.

I've tried to structure the code so that it would work when a dependency is upgraded but i also envision a scenario where Renovate could be used to inflate existing charts used in kustomize kind of like how Renovate today can generate a PR to pin docker digests with a "Pin dependencies" PR when using docker:pinDigests.
But i'm not yet comfortable enough with the codebase to dive deeper into what it would take to make that a possibility, so i would greatly appreciate guidance on that.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[micke]

I've run this on a repository with two example kustomization.yaml files, one with "regular" helm charts and one with OCI chart: https://github.com/micke/renovate-kustomize-artifacts

The resulting "regular" helm chart PR: micke/renovate-kustomize-artifacts#15
And the resulting OCI chart PR: micke/renovate-kustomize-artifacts#8

A side effect of having the helm charts inflated is that renovate manages updates for sub-charts and images in these inflated charts.
How should we reason about those? Do we leave it up to the user to exclude/ignore the inflated charts or can and should we do something about that?

[micke]

Would be great to get another review on this!