BDD DSL: Wait for DNS resolution

[sbaum1994]

Why

The EKS features use command-plus-exit-code pairs to wait for newly provisioned gateway names and derived route names to resolve. The DNS name and timeout are the observable contract; retry-loop and resolver syntax are implementation details.

Scope

Add an assertion that an explicit DNS name resolves through the host resolver within an explicit timeout.

Acceptance criteria

• Add the step to the documented DSL catalog.
• Keep the DNS name and timeout visible and support ${VAR} interpolation.
• Use the host resolver consistently with the existing EKS workflow.
• Validate timeout input and avoid unbounded retries.
• Report the unresolved name and timeout without dumping unrelated resolver output.
• Add focused helper, handler, interpolation, timeout, and failure tests.
• Migrate suitable wait-for-dns.sh command pairs without changing gateway-domain derivation.
• Pass affected wiring tests and live EKS feature tests.

Parent: #858