Add tool to extract values from different HelmRelease paths without installing it

What does this MR do and why?

Introduces a tool to help in solving #206 (closed) and #15.
For #206 (closed) we make use of it with parameter --values-path .spec.valuesFrom to get the registry_mirrors from the HelmRelease/sylva-units, without instantiating this HelmRelease (a chicken and egg situation, we need the registry mirrors in order create the Kind cluster on which the HelmRelease would get installed, while we need the Kind cluster to instantiate the HelmRelease and get its values).

What we need to ensure is that for the --values-path .spec.valuesFrom each (Secret or ConfigMap) resource in this HelmRelease.spec.valuesFrom list needs to have contents (at their valuesKey), an empty content would return a None type error.

It's applicability for solving #206 (closed) was already successfully confirmed in multiple ./bootstrap.sh integration testing runs.
CC: @rletrocquer

Related reference(s)

Closes #206 (closed)

Test coverage

[git:fix-issue-206]root@bootstrap-vm:sylva-core- # kustomize build --load-restrictor LoadRestrictionsNone environment-values/rke2-capd-baburciu/ |./tools/extractHelmReleaseValues.py --values-path .spec.valuesFrom | yq .oci_registry_extra_ca_certs
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-----END CERTIFICATE-----
[git:fix-issue-206]root@bootstrap-vm:sylva-core # kustomize build --load-restrictor LoadRestrictionsNone environment-values/rke2-capd-baburciu/ |./tools/extractHelmReleaseValues.py --values-path .spec.chart.spec.valuesFiles
valuesFiles:
- charts/sylva-units/values.yaml
- charts/sylva-units/management.values.yaml

[git:fix-issue-206]root@bootstrap-vm:sylva-core # kustomize build --load-restrictor LoadRestrictionsNone environment-values/rke2-capd-baburciu/ |./tools/extractHelmReleaseValues.py --values-path .spec.values
values:
  source_templates:
    sylva-core:
      existing_source:
        kind: GitRepository
        name: sylva-core

[git:fix-issue-206]root@bootstrap-vm:sylva-core#