feat(rds): support aurora postgresql 14.8 (#26427)

Add Aurora PostgreSQL 14.8 to database cluster engine.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraPostgreSQLReleaseNotes/AuroraPostgreSQL.Updates.html#AuroraPostgreSQL.Updates.20180305.148X

S3 import and s3 export features are supported.

```
$ aws rds describe-db-engine-versions --region us-east-1 --engine aurora-postgresql --engine-version 14.8
{
    "DBEngineVersions": [
        {
            "Engine": "aurora-postgresql",
            "EngineVersion": "14.8",
            "DBParameterGroupFamily": "aurora-postgresql14",
            "DBEngineDescription": "Aurora (PostgreSQL)",
            "DBEngineVersionDescription": "Aurora PostgreSQL (Compatible with PostgreSQL 14.8)",
            "ValidUpgradeTarget": [
                {
                    "Engine": "aurora-postgresql",
                    "EngineVersion": "15.3",
                    "Description": "Aurora PostgreSQL (Compatible with PostgreSQL 15.3)",
                    "AutoUpgrade": false,
                    "IsMajorVersionUpgrade": true,
                    "SupportedEngineModes": [
                        "provisioned"
                    ],
                    "SupportsParallelQuery": false,
                    "SupportsGlobalDatabases": true,
                    "SupportsBabelfish": true
                }
            ],
            "ExportableLogTypes": [
                "postgresql"
            ],
            "SupportsLogExportsToCloudwatchLogs": true,
            "SupportsReadReplica": false,
            "SupportedEngineModes": [
                "provisioned"
            ],
            "SupportedFeatureNames": [
                "Comprehend",
                "Lambda",
                "s3Export",
                "s3Import",
                "SageMaker"
            ],
            "Status": "available",
            "SupportsParallelQuery": false,
            "SupportsGlobalDatabases": true,
            "MajorEngineVersion": "14",
            "SupportsBabelfish": true,
            "SupportsCertificateRotationWithoutRestart": true,
            "SupportedCACertificateIdentifiers": [
                "rds-ca-2019",
                "rds-ca-ecc384-g1",
                "rds-ca-rsa4096-g1",
                "rds-ca-rsa2048-g1"
            ]
        }
    ]
}
```

_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

@@ -710,6 +710,8 @@ export class AuroraPostgresEngineVersion {
   public static readonly VER_14_6 = AuroraPostgresEngineVersion.of('14.6', '14', { s3Import: true, s3Export: true });
   /** Version "14.7". */
   public static readonly VER_14_7 = AuroraPostgresEngineVersion.of('14.7', '14', { s3Import: true, s3Export: true });
+  /** Version "14.8". */
+  public static readonly VER_14_8 = AuroraPostgresEngineVersion.of('14.8', '14', { s3Import: true, s3Export: true });
   /** Version "15.2". */
   public static readonly VER_15_2 = AuroraPostgresEngineVersion.of('15.2', '15', { s3Import: true, s3Export: true });
   /** Version "15.3". */