BDD DSL: Assert Helm release values subsets

[sbaum1994]

Why

Observability features use helm get values piped through JSON and jq to assert release configuration. The release identity and expected values are clearer and safer as a visible YAML subset.

Scope

Add an assertion that a named Helm release contains a supplied YAML values subset using an explicit namespace and Kubernetes context.

Acceptance criteria

• Add the step to the documented DSL catalog.
• Keep the release name, namespace, context, and expected YAML subset visible.
• Reuse the existing YAML subset and ${VAR} interpolation semantics.
• Avoid ambient Kubernetes context.
• Report the release and first differing path without printing actual values or secret-bearing release data.
• Add focused command-construction, matcher, handler, and secret-hygiene tests.
• Migrate suitable helm get values plus jq assertions without weakening their expected values.
• Pass affected wiring tests and live observability feature tests.

Parent: #858