feat(kinesisanalytics-flink): support Apache Flink 1.20 (#31349)

### Issue # (if applicable)

N/A

### Reason for this change
Support new runtime.

Ref: https://aws.amazon.com/about-aws/whats-new/2024/09/amazon-managed-service-apache-flink-1-20/



### Description of changes
* Add Flink 1.20 to enum
* Improve unit tests and integ test to test all runtime versions



### Description of how you validated changes
Ran improved unit tests and integ tests.



### 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/aws-kinesisanalytics-flink-alpha/README.md

@@ -46,7 +46,7 @@ const flinkApp = new flink.Application(this, 'Application', {
     },
   },
   // ...
-  runtime: flink.Runtime.FLINK_1_19,
+  runtime: flink.Runtime.FLINK_1_20,
   code: flink.ApplicationCode.fromBucket(bucket, 'my-app.jar'),
 });
 ```
@@ -59,7 +59,7 @@ snapshotting, monitoring, and parallelism.
 declare const bucket: s3.Bucket;
 const flinkApp = new flink.Application(this, 'Application', {
   code: flink.ApplicationCode.fromBucket(bucket, 'my-app.jar'),
-  runtime: flink.Runtime.FLINK_1_19,
+  runtime: flink.Runtime.FLINK_1_20,
   checkpointingEnabled: true, // default is true
   checkpointInterval: Duration.seconds(30), // default is 1 minute
   minPauseBetweenCheckpoints: Duration.seconds(10), // default is 5 seconds
@@ -80,7 +80,7 @@ declare const bucket: s3.Bucket;
 declare const vpc: ec2.Vpc;
 const flinkApp = new flink.Application(this, 'Application', {
   code: flink.ApplicationCode.fromBucket(bucket, 'my-app.jar'),
-  runtime: flink.Runtime.FLINK_1_19,
+  runtime: flink.Runtime.FLINK_1_20,
   vpc,
 });
 ```

packages/@aws-cdk/aws-kinesisanalytics-flink-alpha/lib/types.ts

@@ -72,6 +72,9 @@ export class Runtime {
   /** Flink Version 1.19 */
   public static readonly FLINK_1_19 = Runtime.of('FLINK-1_19');
 
+  /** Flink Version 1.20 */
+  public static readonly FLINK_1_20 = Runtime.of('FLINK-1_20');
+
   /** Create a new Runtime with with an arbitrary Flink version string */
   public static of(value: string) {
     return new Runtime(value);

packages/@aws-cdk/aws-kinesisanalytics-flink-alpha/test/application.test.ts

@@ -21,21 +21,32 @@ describe('Application', () => {
     stack = new core.Stack();
     bucket = new s3.Bucket(stack, 'CodeBucket');
     requiredProps = {
-      runtime: flink.Runtime.FLINK_1_19,
+      runtime: flink.Runtime.FLINK_1_20,
       code: flink.ApplicationCode.fromBucket(bucket, 'my-app.jar'),
     };
   });
 
-  test('default Flink Application', () => {
+  const flinkRuntimes = [
+    flink.Runtime.FLINK_1_6,
+    flink.Runtime.FLINK_1_8,
+    flink.Runtime.FLINK_1_11,
+    flink.Runtime.FLINK_1_13,
+    flink.Runtime.FLINK_1_15,
+    flink.Runtime.FLINK_1_18,
+    flink.Runtime.FLINK_1_19,
+    flink.Runtime.FLINK_1_20,
+  ];
+
+  test.each(flinkRuntimes)('Flink Application with %s', (runtime) => {
     new flink.Application(stack, 'FlinkApplication', {
-      runtime: flink.Runtime.FLINK_1_19,
+      runtime,
       code: flink.ApplicationCode.fromBucket(bucket, 'my-app.jar'),
       applicationName: 'MyFlinkApplication',
     });
 
     Template.fromStack(stack).hasResourceProperties('AWS::KinesisAnalyticsV2::Application', {
       ApplicationName: 'MyFlinkApplication',
-      RuntimeEnvironment: 'FLINK-1_19',
+      RuntimeEnvironment: runtime.value,
       ServiceExecutionRole: {
         'Fn::GetAtt': [
           'FlinkApplicationRole2F7BCBF6',