Complete E2E coverage for core GA resources

[shreemaan-abhishek]

Part of #22.

Ensure full CRUD-roundtrip E2E (create → read-back+assert → update → read-back+assert → delete → verify cleanup) for: context, gateway-group, service, route, consumer, credential, ssl, secret, global-rule, plugin, plugin-metadata, proto, and config validate/dump/diff/sync.

• No data-plane traffic forwarding tests (stays in the gateway repo).
• Shared/global resources (global-rule, plugin-metadata, ssl, secret): use unique resource IDs and aggressive cleanup to avoid shared-dev-env collisions.

[coderabbitai]

🔗 Related PRs

#2 - test: align E2E coverage with current EE models [merged]
#3 - test: migrate runtime coverage toward ginkgo e2e [merged]
#6 - test: strengthen E2E readback assertions [merged]
#20 - fix update commands to preserve full PUT payloads [merged]

---

📝 Issue Planner

_{Check the box below or use the @coderabbitai plan command to generate an implementation plan and prompts that you can use with your favorite coding assistant.}

• Create Plan

---

🧪 Issue enrichment is currently in open beta.

You can configure auto-planning by selecting labels in the issue_enrichment configuration.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

💬 Have feedback or questions? Drop into our discord!