chore(rds): add latest Aurora MySQL and Aurora PostgreSQL engine versions

[rgoltz]

Issue # (if applicable)

Closes #37200.

Reason for this change

New Aurora engine versions have been released by AWS and are missing from the CDK's version constants.

Description of changes

Added new version constants to packages/aws-cdk-lib/aws-rds/lib/cluster-engine.ts:

Aurora PostgreSQL:

• VER_14_22
• VER_15_17
• VER_16_13
• VER_17_9

Aurora MySQL:

• VER_2_12_6
• VER_3_10_4

Describe any new or updated permissions being added

N/A

Description of how you validated changes

Verified via AWS CLI that the new versions are available:

$ aws rds describe-db-engine-versions --engine aurora-postgresql --query "DBEngineVersions[].EngineVersion" --output text 2>/dev/null | tr '\t' '\n' | sort -V
...
14.20
14.22
...
15.15
15.17
...
16.11
16.11-limitless
16.13
...
17.7
17.9

$ aws rds describe-db-engine-versions --engine aurora-mysql --query "DBEngineVersions[].EngineVersion" --output text 2>/dev/null | tr '\t' '\n' | sort -V
...
5.7.mysql_aurora.2.12.5
5.7.mysql_aurora.2.12.6
...
8.0.mysql_aurora.3.10.3
8.0.mysql_aurora.3.10.4
...

Note: No README, test, or snapshot changes required. This PR only adds new version constants following the existing pattern. Integration tests use a getLatestVersion() helper in packages/@aws-cdk-testing/framework-integ/test/aws-rds/test/db-versions.ts that dynamically resolves the highest version at runtime — new versions are automatically covered.

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