🤖 Add Helm chart unit tests

[arybolovlev]

Description

Add Helm chart unit tests using Terratest. While Terratest is currently used to render manifests from the Helm chart, this may be excessive for our needs. In the future, consider transitioning to the Helm SDK to simplify and streamline the process.

Usage Example

Terratest

$ make test-helm
...
PASS
ok  	github.com/hashicorp/hcp-terraform-operator/charts/test/unit	2.207s

References

N/A.

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