feat(redshift): update default node type from DC2_LARGE to RA3_LARGE

[badmintoncryer]

Issue # (if applicable)

Closes #36416.

Reason for this change

Redshift doesn't support for creating dc2 instance type now. However, AWS CDK uses dc2.large node type as a default value. Therefore, we cannot deploy Redshift cluster with minimum configuration.

declare const vpc: ec2.IVpc;

const cluster = new Cluster(this, 'Redshift', {
  masterUser: {
    masterUsername: 'admin',
  },
  vpc,
});

Description of changes

Update the default node type to ra3.large that is now recommended by AWS.

Describe any new or updated permissions being added

none

Description of how you validated changes

Update existing unit and integ tests.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

BREAKING CHANGE: Updated default nodeType. Previously, DC2.LARGE is used, but after the correction, new default nodeType is RA3.LARGE.

[aws-cdk-automation]

(This review is outdated)

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ☑️	Skipped	Failed ❌️
Security Guardian Results	325 ran	324 passed		1 failed

Test	Result
Security Guardian Results
packages/@aws-cdk/aws-redshift-alpha/test/integ.cluster-loggingbucket.js.snapshot/awscdkredshiftclusterdatabaseredshiftloggingbucketinteg06BC94A7.template.json
s3-encryption-enabled.guard	❌ failure

• View Security Guardian Results

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ☑️	Skipped	Failed ❌️
Security Guardian Results with resolved templates	325 ran	324 passed		1 failed

Test	Result
Security Guardian Results with resolved templates
packages/@aws-cdk/aws-redshift-alpha/test/integ.cluster-loggingbucket.js.snapshot/awscdkredshiftclusterdatabaseredshiftloggingbucketinteg06BC94A7.template.json
s3-encryption-enabled.guard	❌ failure

• View Security Guardian Results with resolved templates

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.