chore(rds): support 5.7.44-rds.20240808 for RDS for MySQL (#31260)

Add new instance engine.

Ref: [Amazon RDS for MySQL announces Extended Support minor 5.7.44-RDS.20240808](https://aws.amazon.com/about-aws/whats-new/2024/08/amazon-rds-mysql-extended-support-minor-5-7-44-rds-20240808/)

```sh
% aws rds describe-db-engine-versions --engine mysql --query "DBEngineVersions[].EngineVersion" --output table --region us-east-1
--------------------------
|DescribeDBEngineVersions|
+------------------------+
|  5.7.44                |
|  5.7.44-rds.20240408   |
|  5.7.44-rds.20240529   |
|  5.7.44-rds.20240808   | // this
|  8.0.32                |
|  8.0.33                |
|  8.0.34                |
|  8.0.35                |
|  8.0.36                |
|  8.0.37                |
|  8.0.39                |
+------------------------+
```

### 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/instance-engine.ts

@@ -841,6 +841,8 @@ export class MysqlEngineVersion {
   public static readonly VER_5_7_44_RDS_20240408 = MysqlEngineVersion.of('5.7.44-rds.20240408', '5.7');
   /** Version "5.7.44-rds.20240529". */
   public static readonly VER_5_7_44_RDS_20240529 = MysqlEngineVersion.of('5.7.44-rds.20240529', '5.7');
+  /** Version "5.7.44-rds.20240808". */
+  public static readonly VER_5_7_44_RDS_20240808 = MysqlEngineVersion.of('5.7.44-rds.20240808', '5.7');
 
   /** Version "8.0" (only a major version, without a specific minor version). */
   public static readonly VER_8_0 = MysqlEngineVersion.of('8.0', '8.0');