chore(rds): add MySQL version 8.4.7 (#36022)

### Reason for this change

A new MySQL engine version is available.

No announcements are published yet.

### Description of changes

- Added a MySQL engine version 8.4.7

### Describe any new or updated permissions being added

N/A

### Description of how you validated changes

``` console
$ aws --region us-east-1 rds describe-db-engine-versions --engine 'mysql' --query 'DBEngine
Versions[].EngineVersion' --output table
--------------------------
|DescribeDBEngineVersions|
+------------------------+
|  5.7.44-rds.20240408   |
|  5.7.44-rds.20240529   |
|  5.7.44-rds.20240808   |
|  5.7.44-rds.20250103   |
|  5.7.44-rds.20250213   |
|  5.7.44-rds.20250508   |
|  5.7.44-rds.20250818   |
|  8.0.37                |
|  8.0.39                |
|  8.0.40                |
|  8.0.41                |
|  8.0.42                |
|  8.0.43                |
|  8.4.3                 |
|  8.4.4                 |
|  8.4.5                 |
|  8.4.6                 |
|  8.4.7                 |
+------------------------+
```


### 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*

Author: Tietew

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

@@ -1020,6 +1020,8 @@ export class MysqlEngineVersion {
   public static readonly VER_8_4_5 = MysqlEngineVersion.of('8.4.5', '8.4');
   /** Version "8.4.6". */
   public static readonly VER_8_4_6 = MysqlEngineVersion.of('8.4.6', '8.4');
+  /** Version "8.4.7". */
+  public static readonly VER_8_4_7 = MysqlEngineVersion.of('8.4.7', '8.4');
 
   /**
    * Create a new MysqlEngineVersion with an arbitrary version.