fix(helm): support multiple resources in one template

[phooijenga]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Description

The output of the helm template command is a multi-document YAML stream. Each document starts with a --- marker. However, Helm templates can also contain multiple documents.

Currently, this results in a (mostly silent) "error parsing output". The remaining resources are not scanned.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes