feat(synthetics): add syn-nodejs-3.0 runtime

Adds the missing `SYNTHETICS_NODEJS_3_0` runtime constant to the Runtime class.
This runtime is based on Node.js 20.x and supports the multi-checks blueprint
for creating synthetic monitoring scenarios without browser/framework dependencies.

Fixes #36648

Author: OlegHQ

packages/aws-cdk-lib/aws-synthetics/lib/runtime.ts

@@ -360,6 +360,17 @@ export class Runtime {
    */
   public static readonly SYNTHETICS_NODEJS_PLAYWRIGHT_3_0 = new Runtime('syn-nodejs-playwright-3.0', RuntimeFamily.NODEJS);
 
+  /**
+   * `syn-nodejs-3.0` includes the following:
+   * - Lambda runtime Node.js 20.x
+   *
+   * New Features:
+   * - **Multi-checks blueprint**: Supports the multi-checks blueprint for creating complex synthetic monitoring scenarios.
+   *
+   * @see https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Library_Nodejs.html
+   */
+  public static readonly SYNTHETICS_NODEJS_3_0 = new Runtime('syn-nodejs-3.0', RuntimeFamily.NODEJS);
+
   /**
    * `syn-python-selenium-1.0` includes the following:
    * - Lambda runtime Python 3.8