feat(neptune): add engine version 1.1.1.0 (#21079)

Fixes #20869.

Adds new engine version `1.1.1.0` to Neptune.
See https://docs.aws.amazon.com/neptune/latest/userguide/engine-releases.html

As this is just  a new enum value, it would be great if the label `pr-linter/exempt-readme` and `pr-linter/exempt-integ-test` could be added. Thanks!

----

### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md)

### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*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-neptune/lib/cluster.ts

@@ -54,6 +54,10 @@ export class EngineVersion {
    * Neptune engine version 1.1.0.0
    */
   public static readonly V1_1_0_0 = new EngineVersion('1.1.0.0');
+  /**
+   * Neptune engine version 1.1.1.0
+   */
+  public static readonly V1_1_1_0 = new EngineVersion('1.1.1.0');
 
   /**
    * Constructor for specifying a custom engine version

packages/@aws-cdk/aws-neptune/test/cluster.test.ts

@@ -118,6 +118,29 @@ describe('DatabaseCluster', () => {
     });
   });
 
+  test.each([
+    ['1.1.1.0', EngineVersion.V1_1_1_0],
+  ])('can create a cluster for engine version %s', (expected, version) => {
+    // GIVEN
+    const stack = testStack();
+    const vpc = new ec2.Vpc(stack, 'VPC');
+
+    // WHEN
+    new DatabaseCluster(stack, 'Database', {
+      vpc,
+      instanceType: InstanceType.R5_LARGE,
+      engineVersion: version,
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::Neptune::DBCluster', {
+      EngineVersion: expected,
+      DBSubnetGroupName: { Ref: 'DatabaseSubnets3C9252C9' },
+      VpcSecurityGroupIds: [{ 'Fn::GetAtt': ['DatabaseSecurityGroup5C91FDCB', 'GroupId'] }],
+    });
+  });
+
+
   test('can create a cluster with imported vpc and security group', () => {
     // GIVEN
     const stack = testStack();