feat(acm): validated certificate can use existing Role

[rix0rrr]

Allow specifying an existing Role for the Validated Certificate,
to remove the dependency on iam:CreateRole.

Fixes #3519, but needs implementation of #3753 for maximum usefulness.

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[mergify]

Pull Request Checklist

• Testing

• Unit test added (prefer to add a new test rather than modify existing tests)
• CLI change? Re-run/add CLI integration tests

• Documentation

• Inline docs: make sure all public APIs are documented (copy & paste from official AWS docs)
• README: update module README
• Design: for significant features, follow the design process

• Title uses the format type(scope): text

• Type: fix, feat, refactor go into CHANGELOG, chore is hidden
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• Breaking?: last paragraph: BREAKING CHANGE: <describe what changed + link for details>

• Sensitive Modules (requires 2 PR approvers)

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• Grant APIs (if not based on official documentation with a reference)

[shivlaks]

any reason not to use a 12 digit placeholder account id?

[rix0rrr]

Not particularly.

[mergify]

Thanks so much for taking the time to contribute to the AWS CDK ❤️

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checklist:

• PR title type(scope): text
  • type: fix, feat, refactor go into CHANGELOG, chore is hidden
  • scope: name of module without aws- or cdk- prefix or postfix (e.g. s3 instead of aws-s3-deployment)
  • text: use all lower-case, do not end with a period, do not include issue refs
• PR Description
  • Rationale: describe rationale of change and approach taken
  • Issues: indicate issues fixed via: fixes #xxx or closes #xxx
  • Breaking?: last paragraph: BREAKING CHANGE: <describe what changed + link for details>
• Testing
  • Unit test added. Prefer to add a new test rather than modify existing tests
  • CLI or init templates change? Re-run/add CLI integration tests
• Documentation
  • README: update module README to describe new features
  • API docs: public APIs must be documented. Copy from official AWS docs when possible
  • Design: for significant features, follow design process