chore(rds): add support for aurora-postgresql 16.3 (#31003)

### Reason for this change

Add support for newly supported aurora-postgresql16 16.3.

### Description of changes

Add a new version as a new property to AuroraPostgresEngineVersion class. (see https://docs.aws.amazon.com/AmazonRDS/latest/PostgreSQLReleaseNotes/postgresql-versions.html)
The change already happened with #30242 and was reverted by #30296 as the version was not available.

### Description of how you validated changes

The version 16.3 is available now:

```bash
$ aws rds describe-db-engine-versions --engine aurora-postgresql --query "DBEngineVersions[?EngineVersion=='16.3']"
[
    {
        "Engine": "aurora-postgresql",
        "EngineVersion": "16.3",
        "DBParameterGroupFamily": "aurora-postgresql16",
        "DBEngineDescription": "Aurora (PostgreSQL)",
        "DBEngineVersionDescription": "Aurora PostgreSQL (Compatible with PostgreSQL 16.3)",
        "ValidUpgradeTarget": [],
        "ExportableLogTypes": [
            "postgresql"
        ],
        "SupportsLogExportsToCloudwatchLogs": true,
        "SupportsReadReplica": false,
        "SupportedEngineModes": [
            "provisioned"
        ],
        "SupportedFeatureNames": [
            "Comprehend",
            "Lambda",
            "s3Export",
            "s3Import",
            "SageMaker"
        ],
        "Status": "available",
        "SupportsParallelQuery": false,
        "SupportsGlobalDatabases": true,
        "MajorEngineVersion": "16",
        "SupportsBabelfish": true,
        "SupportsLimitlessDatabase": false,
        "SupportsCertificateRotationWithoutRestart": true,
        "SupportedCACertificateIdentifiers": [
            "rds-ca-2019",
            "rds-ca-ecc384-g1",
            "rds-ca-rsa4096-g1",
            "rds-ca-rsa2048-g1"
        ],
        "SupportsLocalWriteForwarding": true,
        "SupportsIntegrations": false
    }
]

```

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

packages/aws-cdk-lib/aws-rds/lib/cluster-engine.ts

@@ -1019,6 +1019,8 @@ export class AuroraPostgresEngineVersion {
   public static readonly VER_16_1 = AuroraPostgresEngineVersion.of('16.1', '16', { s3Import: true, s3Export: true });
   /** Version "16.2". */
   public static readonly VER_16_2 = AuroraPostgresEngineVersion.of('16.2', '16', { s3Import: true, s3Export: true });
+  /** Version "16.3". */
+  public static readonly VER_16_3 = AuroraPostgresEngineVersion.of('16.3', '16', { s3Import: true, s3Export: true });
 
   /**
    * Create a new AuroraPostgresEngineVersion with an arbitrary version.

packages/aws-cdk-lib/aws-rds/test/cluster-engine.test.ts

@@ -106,6 +106,8 @@ describe('cluster engine', () => {
       'aurora-postgresql10');
     expect(DatabaseClusterEngine.auroraPostgres({ version: AuroraPostgresEngineVersion.of('14.3', '14') }).parameterGroupFamily).toEqual(
       'aurora-postgresql14');
+    expect(DatabaseClusterEngine.auroraPostgres({ version: AuroraPostgresEngineVersion.of('16.3', '16') }).parameterGroupFamily).toEqual(
+      'aurora-postgresql16');
   });
 
   test('supported log types', () => {