message: Add EventBridge message mapping
diff: @@ -175,6 +175,8 @@ So in the above example, the `target1` function doesn't use the `timeout` that i
  Configure the internally created CDK `Target`.
  ```js {8-10}
  +import { RuleTargetInput } from '@aws-cdk/aws-events';
  +
  new EventBus(this, "Bus", {
  rules: {
  rule1: {
  @@ -184,6 +186,7 @@ new EventBus(this, "Bus", {
  function: "src/target1.main",
  targetProps: {
  retryAttempts: 20,
  + message: RuleTargetInput.fromEventPath('$.detail'),
  },
  },
  ],
  @@ -191,6 +194,7 @@ new EventBus(this, "Bus", {
  },
  });
  ```
  +In the example above, the function is invoked with the contents of the `detail` property on the event, instead of the envelope - i.e. the original payload put onto the EventBus.
  #### Attaching permissions for all targets
  