chore(rds): upgrade rds(PostgreSQL) version (#25772)

[Amazon RDS for PostgreSQL supports minor versions 15.3, 14.8, 13.11, 12.15, and 11.20](https://aws.amazon.com/about-aws/whats-new/2023/05/amazon-rds-postgresql-supports-new-minor-versions/)

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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*

Author: watany-dev

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

@@ -1050,6 +1050,8 @@ export class PostgresEngineVersion {
   public static readonly VER_11_18 = PostgresEngineVersion.of('11.18', '11', { s3Import: true, s3Export: true });
   /** Version "11.19". */
   public static readonly VER_11_19 = PostgresEngineVersion.of('11.19', '11', { s3Import: true, s3Export: true });
+  /** Version "11.20". */
+  public static readonly VER_11_20 = PostgresEngineVersion.of('11.20', '11', { s3Import: true, s3Export: true });
 
   /** Version "12" (only a major version, without a specific minor version). */
   public static readonly VER_12 = PostgresEngineVersion.of('12', '12', { s3Import: true });
@@ -1079,6 +1081,8 @@ export class PostgresEngineVersion {
   public static readonly VER_12_13 = PostgresEngineVersion.of('12.13', '12', { s3Import: true, s3Export: true });
   /** Version "12.14". */
   public static readonly VER_12_14 = PostgresEngineVersion.of('12.14', '12', { s3Import: true, s3Export: true });
+  /** Version "12.15". */
+  public static readonly VER_12_15 = PostgresEngineVersion.of('12.15', '12', { s3Import: true, s3Export: true });
 
   /** Version "13" (only a major version, without a specific minor version). */
   public static readonly VER_13 = PostgresEngineVersion.of('13', '13', { s3Import: true, s3Export: true });
@@ -1102,6 +1106,8 @@ export class PostgresEngineVersion {
   public static readonly VER_13_9 = PostgresEngineVersion.of('13.9', '13', { s3Import: true, s3Export: true });
   /** Version "13.10". */
   public static readonly VER_13_10 = PostgresEngineVersion.of('13.10', '13', { s3Import: true, s3Export: true });
+  /** Version "13.11". */
+  public static readonly VER_13_11 = PostgresEngineVersion.of('13.11', '13', { s3Import: true, s3Export: true });
 
   /** Version "14" (only a major version, without a specific minor version). */
   public static readonly VER_14 = PostgresEngineVersion.of('14', '14', { s3Import: true, s3Export: true });
@@ -1119,11 +1125,15 @@ export class PostgresEngineVersion {
   public static readonly VER_14_6 = PostgresEngineVersion.of('14.6', '14', { s3Import: true, s3Export: true });
   /** Version "14.7". */
   public static readonly VER_14_7 = PostgresEngineVersion.of('14.7', '14', { s3Import: true, s3Export: true });
+  /** Version "14.8". */
+  public static readonly VER_14_8 = PostgresEngineVersion.of('14.8', '14', { s3Import: true, s3Export: true });
 
   /** Version "15" (only a major version, without a specific minor version). */
   public static readonly VER_15 = PostgresEngineVersion.of('15', '15', { s3Import: true, s3Export: true });
   /** Version "15.2". */
   public static readonly VER_15_2 = PostgresEngineVersion.of('15.2', '15', { s3Import: true, s3Export: true });
+  /** Version "15.3". */
+  public static readonly VER_15_3 = PostgresEngineVersion.of('15.3', '15', { s3Import: true, s3Export: true });
 
   /**
    * Create a new PostgresEngineVersion with an arbitrary version.