feat(network-disruption): add DNS resolver control

[aymericDD]

What does this PR do?

• [x] Adds new functionality
• [ ] Alters existing functionality
• [ ] Fixes a bug
• [ ] Improves documentation or testing

Please briefly describe your changes as well as the motivation behind them:

Changes:

• Adds per-host DNS resolution strategy control through a new dnsResolver field on network disruption hosts
• Implements four DNS resolver strategies: pod, node, pod-fallback-node (default), and node-fallback-pod
• Refactors DNS client to support strategy-based resolution with ResolveWithStrategy method
• Adds getResolversAndNames helper method for cleaner DNS configuration logic

Motivation:

• Addresses issues with service mesh proxies (like Istio DNS proxy) that intercept DNS queries and return VIP addresses (240.x.x.x) that don't work with tc traffic control rules
• Provides flexibility for users to choose between pod and node nameservers based on their cluster configuration
• Maintains backward compatibility with default pod-fallback-node strategy

Resolves: #882

Code Quality Checklist

• [x] The documentation is up to date.
• [x] My code is sufficiently commented and passes continuous integration checks.
• [x] I have signed my commit (see Contributing Docs).

Testing

• [x] I leveraged continuous integration testing
  • [x] by depending on existing unit tests or end-to-end tests.
  • [x] by adding new unit tests or end-to-end tests.
• [x] I manually tested the following steps:
  • Test default behavior without specifying dnsResolver field (uses pod-fallback-node)
  • Test dnsResolver: pod strategy to verify pod-only DNS resolution
  • Test dnsResolver: node strategy to verify node-only DNS resolution
  • Test dnsResolver: pod-fallback-node with pod DNS failure to verify fallback
  • Test dnsResolver: node-fallback-pod with node DNS failure to verify fallback
  • Test with Istio-enabled namespace using dnsResolver: node to bypass DNS proxy
  • [x] locally.
  • [ ] as a canary deployment to a cluster.

[aymericDD]

• #1012
• #1011
• #1010
• #1009 👈 (View in Graphite)
• main

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[datadog-datadog-prod-us1[bot]]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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