chore(neptune): add engine versions 1.2.0.1 , 1.2.0.2 & 1.2.1.0 (#25209)

Add the following Neptune engine versions:

- `1.2.0.1` - https://docs.aws.amazon.com/neptune/latest/userguide/engine-releases-1.2.0.1.html
- `1.2.0.2` - https://docs.aws.amazon.com/neptune/latest/userguide/engine-releases-1.2.0.2.html
- `1.2.1.0` - https://docs.aws.amazon.com/neptune/latest/userguide/engine-releases-1.2.1.0.html

Closes #25208.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: gopuneet

packages/@aws-cdk/aws-neptune-alpha/lib/cluster.ts

@@ -64,6 +64,18 @@ export class EngineVersion {
    * Neptune engine version 1.2.0.0
    */
   public static readonly V1_2_0_0 = new EngineVersion('1.2.0.0');
+  /**
+   * Neptune engine version 1.2.0.1
+   */
+  public static readonly V1_2_0_1 = new EngineVersion('1.2.0.1');
+  /**
+   * Neptune engine version 1.2.0.2
+   */
+  public static readonly V1_2_0_2 = new EngineVersion('1.2.0.2');
+  /**
+   * Neptune engine version 1.2.1.0
+   */
+  public static readonly V1_2_1_0 = new EngineVersion('1.2.1.0');
 
   /**
    * Constructor for specifying a custom engine version