feat: emr instance fleet priority allocation

[Daniel-ZA]

Issue # (if applicable)

Closes #35710

Reason for this change

The CDK's OnDemandAllocationStrategy enum only includes LOWEST_PRICE, but AWS EMR supports a prioritized allocation strategy that allows users to specify instance type priorities. This enhancement aligns the CDK with the full EMR API capabilities.

Description of changes

1. Add PRIORITIZED = 'prioritized' to the OnDemandAllocationStrategy enum
2. Add an optional priority?: number field to InstanceTypeConfigProperty
3. Update the InstanceTypeConfigPropertyToJson function to map the priority field to the CloudFormation output
4. Added comprehensive unit tests covering enum values, priority field usage, and CloudFormation template generation
5. Added integration test demonstrating real-world usage with multiple instance types and priorities

Describe any new or updated permissions being added

No new IAM permissions are required. This change only extends existing EMR cluster creation functionality with additional configuration options.

Description of how you validated changes

• Unit tests: Added 3 tests covering enum values, priority field functionality, and CloudFormation output validation
• Integration test: Created end-to-end test with realistic EMR cluster configuration using prioritized allocation strategy
• Manual validation: Verified CloudFormation templates generate correctly with AllocationStrategy: "prioritized" and Priority: N fields
• Backward compatibility: Confirmed existing tests continue to pass without modification

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[aws-cdk-automation]

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[aws-cdk-automation]

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

[pahud]

This PR is now in the needs-community-review queue. Once it receives an approving community review, it will move to the needs-maintainer-review stage for final approval. Feel free to continue improve this PR when necessary. Make sure CI passes with no conflicts after each commit. Thank you.

[pahud]

What I like:
Minimal, surgical changes — enum addition, optional priority field, and serialization update. Zero breaking changes.
Unit tests cover enum values, priority field usage, and CloudFormation template output.
Integration test with a realistic prioritized instance fleet scenario.
README updated with a clear code example.

Minor nits (non-blocking):
The priority JSDoc could include a @see link to the EMR InstanceTypeConfig API reference for discoverability.
A few snapshot files are missing a trailing newline (No newline at end of file).

Suggestion for consideration:
There's currently no CDK-level validation to warn users when allocationStrategy is PRIORITIZED but priority is not set on instanceTypeConfigs. EMR will reject it at deploy time, but an early validation (or at minimum a note in the JSDoc) could save users a round-trip. This could also be a follow-up — not necessarily a blocker for this PR.

Overall this looks good to me. Approving for community review. 👍

Pull request has been modified.