chore: add nag tests to examples

[vgkowski]

Issue #, if available:

Description of changes:

• Add CDK_nag tests to examples
• Add NAG suppressions in examples for resources already tested as part of the framework
• Change service level role scope in OpenSearch construct to put it under the Domain scope

Checklist

* [x] Update tests * [ ] Update docs * [x] PR title follows [conventional commit semantics](https://www.conventionalcommits.org/en/v1.0.0/) (`fix: `, `feat: `, `docs: `, ...) ## Breaking change checklist

RFC issue #:

• [ ] Migration process documented
• [ ] Implement warnings (if it can live side by side)

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