feat(rds): support local write forwarding for an aurora PostgreSQL cl…

…uster (aws#31803)

### Issue # (if applicable)

Closes aws#31802.

### Reason for this change



Amazon Aurora PostgreSQL now supports local write forwarding:

Whats new: https://aws.amazon.com/about-aws/whats-new/2024/10/amazon-aurora-postgresql-local-write-forwarding/

Reference: https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-postgresql-write-forwarding.html

The current CDK L2 construct only supports MySQL, but PostgreSQL needs to be supported as well.

### Description of changes



Remove the validation that engineType is either aurora or aurora-mysql, and modify docs.

### Description of how you validated changes



Both unit tests and an integ test.

### 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-testing/framework-integ/test/aws-rds/test/integ.cluster-enable-local-write-forwarding.js.snapshot/EnableLocalWriteForwardingClusterStack.template.json

@@ -670,6 +670,163 @@
    ],
    "UpdateReplacePolicy": "Delete",
    "DeletionPolicy": "Delete"
+  },
+  "DatabaseClusterPostgresqlSubnetsE0173DAA": {
+   "Type": "AWS::RDS::DBSubnetGroup",
+   "Properties": {
+    "DBSubnetGroupDescription": "Subnets for DatabaseClusterPostgresql database",
+    "SubnetIds": [
+     {
+      "Ref": "VPCPrivateSubnet1Subnet8BCA10E0"
+     },
+     {
+      "Ref": "VPCPrivateSubnet2SubnetCFCDAA7A"
+     }
+    ]
+   }
+  },
+  "DatabaseClusterPostgresqlSecurityGroupEF4103D2": {
+   "Type": "AWS::EC2::SecurityGroup",
+   "Properties": {
+    "GroupDescription": "RDS security group",
+    "SecurityGroupEgress": [
+     {
+      "CidrIp": "0.0.0.0/0",
+      "Description": "Allow all outbound traffic by default",
+      "IpProtocol": "-1"
+     }
+    ],
+    "VpcId": {
+     "Ref": "VPCB9E5F0B4"
+    }
+   }
+  },
+  "DatabaseClusterPostgresqlSecretD2D9C157": {
+   "Type": "AWS::SecretsManager::Secret",
+   "Properties": {
+    "Description": {
+     "Fn::Join": [
+      "",
+      [
+       "Generated by the CDK for stack: ",
+       {
+        "Ref": "AWS::StackName"
+       }
+      ]
+     ]
+    },
+    "GenerateSecretString": {
+     "ExcludeCharacters": " %+~`#$&*()|[]{}:;<>?!'/@\"\\",
+     "GenerateStringKey": "password",
+     "PasswordLength": 30,
+     "SecretStringTemplate": "{\"username\":\"postgres\"}"
+    }
+   },
+   "UpdateReplacePolicy": "Delete",
+   "DeletionPolicy": "Delete"
+  },
+  "DatabaseClusterPostgresqlSecretAttachment09D32DC9": {
+   "Type": "AWS::SecretsManager::SecretTargetAttachment",
+   "Properties": {
+    "SecretId": {
+     "Ref": "DatabaseClusterPostgresqlSecretD2D9C157"
+    },
+    "TargetId": {
+     "Ref": "DatabaseClusterPostgresql0775776E"
+    },
+    "TargetType": "AWS::RDS::DBCluster"
+   }
+  },
+  "DatabaseClusterPostgresql0775776E": {
+   "Type": "AWS::RDS::DBCluster",
+   "Properties": {
+    "CopyTagsToSnapshot": true,
+    "DBClusterParameterGroupName": "default.aurora-postgresql16",
+    "DBSubnetGroupName": {
+     "Ref": "DatabaseClusterPostgresqlSubnetsE0173DAA"
+    },
+    "EnableLocalWriteForwarding": true,
+    "Engine": "aurora-postgresql",
+    "EngineVersion": "16.4",
+    "MasterUserPassword": {
+     "Fn::Join": [
+      "",
+      [
+       "{{resolve:secretsmanager:",
+       {
+        "Ref": "DatabaseClusterPostgresqlSecretD2D9C157"
+       },
+       ":SecretString:password::}}"
+      ]
+     ]
+    },
+    "MasterUsername": {
+     "Fn::Join": [
+      "",
+      [
+       "{{resolve:secretsmanager:",
+       {
+        "Ref": "DatabaseClusterPostgresqlSecretD2D9C157"
+       },
+       ":SecretString:username::}}"
+      ]
+     ]
+    },
+    "Port": 5432,
+    "ServerlessV2ScalingConfiguration": {
+     "MaxCapacity": 2,
+     "MinCapacity": 0.5
+    },
+    "VpcSecurityGroupIds": [
+     {
+      "Fn::GetAtt": [
+       "DatabaseClusterPostgresqlSecurityGroupEF4103D2",
+       "GroupId"
+      ]
+     }
+    ]
+   },
+   "UpdateReplacePolicy": "Snapshot",
+   "DeletionPolicy": "Snapshot"
+  },
+  "DatabaseClusterPostgresqlwriterInstanceB16652DD": {
+   "Type": "AWS::RDS::DBInstance",
+   "Properties": {
+    "DBClusterIdentifier": {
+     "Ref": "DatabaseClusterPostgresql0775776E"
+    },
+    "DBInstanceClass": "db.serverless",
+    "Engine": "aurora-postgresql",
+    "PromotionTier": 0
+   },
+   "DependsOn": [
+    "VPCPrivateSubnet1DefaultRouteAE1D6490",
+    "VPCPrivateSubnet1RouteTableAssociation347902D1",
+    "VPCPrivateSubnet2DefaultRouteF4F5CFD2",
+    "VPCPrivateSubnet2RouteTableAssociation0C73D413"
+   ],
+   "UpdateReplacePolicy": "Delete",
+   "DeletionPolicy": "Delete"
+  },
+  "DatabaseClusterPostgresqlreaderInstance10798C6B0": {
+   "Type": "AWS::RDS::DBInstance",
+   "Properties": {
+    "DBClusterIdentifier": {
+     "Ref": "DatabaseClusterPostgresql0775776E"
+    },
+    "DBInstanceClass": "db.serverless",
+    "Engine": "aurora-postgresql",
+    "PromotionTier": 2
+   },
+   "DependsOn": [
+    "DatabaseClusterPostgresqlwriterInstanceB16652DD",
+    "VPCPrivateSubnet1DefaultRouteAE1D6490",
+    "VPCPrivateSubnet1RouteTableAssociation347902D1",
+    "VPCPrivateSubnet2DefaultRouteF4F5CFD2",
+    "VPCPrivateSubnet2RouteTableAssociation0C73D413"
+   ],
+   "UpdateReplacePolicy": "Delete",
+   "DeletionPolicy": "Delete"
   }
  },
  "Mappings": {