feat(elbv2) expose connection_termination attribute on network target group (#20821)

This adds `deregistration_delay.connection_termination.enabled` attribute to the `NetworkTargetGroupProps` as `connectionTermination`. This is [specific to Network Load balancers](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-elasticloadbalancingv2-targetgroup-targetgroupattribute.html).

I have added integration tests and unit tests.

closes #17010
----

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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: michaeldrey

packages/@aws-cdk/aws-elasticloadbalancingv2/lib/nlb/network-target-group.ts

@@ -51,6 +51,15 @@ export interface NetworkTargetGroupProps extends BaseTargetGroupProps {
    * @default - No targets.
    */
   readonly targets?: INetworkLoadBalancerTarget[];
+
+  /**
+   *
+   * Indicates whether the load balancer terminates connections at
+   * the end of the deregistration timeout.
+   *
+   * @default false
+   */
+  readonly connectionTermination?: boolean;
 }
 
 /**
@@ -93,7 +102,9 @@ export class NetworkTargetGroup extends TargetGroupBase implements INetworkTarge
     if (props.preserveClientIp !== undefined) {
       this.setAttribute('preserve_client_ip.enabled', props.preserveClientIp ? 'true' : 'false');
     }
-
+    if (props.connectionTermination !== undefined) {
+      this.setAttribute('deregistration_delay.connection_termination.enabled', props.connectionTermination ? 'true' : 'false');
+    }
     this.addTarget(...(props.targets || []));
   }
 

packages/@aws-cdk/aws-elasticloadbalancingv2/package.json

@@ -82,6 +82,7 @@
   "devDependencies": {
     "@aws-cdk/assertions": "0.0.0",
     "@aws-cdk/cdk-build-tools": "0.0.0",
+    "@aws-cdk/integ-tests": "0.0.0",
     "@aws-cdk/integ-runner": "0.0.0",
     "@aws-cdk/cfn2ts": "0.0.0",
     "@aws-cdk/pkglint": "0.0.0",