feat(cloudwatch): liveData in GraphWidget (#8579)

CDK is missing support for `liveData` property in GraphWidget. The properties are defined [here](https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/CloudWatch-Dashboard-Body-Structure.html) under "Metric Widget Object."

The optional properties `period` and `stat` are also not supported in Cloudwatch currently. I wonder if there are use cases for those as well.

This PR adds `liveData` to `GraphWidgetProps` and defaults to `false`. It fixes #8376 .

----

*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-cloudwatch/README.md

@@ -252,6 +252,17 @@ dashboard.addWidgets(new GraphWidget({
 }));
 ```
 
+The graph can publish live data within the last minute that has not been fully aggregated.
+
+```ts
+dashboard.addWidgets(new GraphWidget({
+  // ...
+  // ...
+
+  liveData: true,
+}));
+```
+
 ### Alarm widget
 
 An alarm widget shows the graph and the alarm line of a single alarm:

packages/@aws-cdk/aws-cloudwatch/lib/graph.ts

@@ -180,6 +180,13 @@ export interface GraphWidgetProps extends MetricWidgetProps {
    * @default - bottom
    */
   readonly legendPosition?: LegendPosition;
+
+  /**
+   * Whether the graph should show live data
+   *
+   * @default false
+   */
+  readonly liveData?: boolean;
 }
 
 /**
@@ -218,6 +225,7 @@ export class GraphWidget extends ConcreteWidget {
           right: this.props.rightYAxis !== undefined ? this.props.rightYAxis : undefined,
         },
         legend: this.props.legendPosition !== undefined ? { position: this.props.legendPosition } : undefined,
+        liveData: this.props.liveData,
       },
     }];
   }

packages/@aws-cdk/aws-cloudwatch/test/test.graphs.ts

@@ -303,6 +303,37 @@ export = {
     test.done();
   },
 
+  'specify liveData property on graph'(test: Test) {
+    // WHEN
+    const stack = new Stack();
+    const widget = new GraphWidget({
+      title: 'My live graph',
+      left: [
+        new Metric({ namespace: 'CDK', metricName: 'Test' }),
+      ],
+      liveData: true,
+    });
+
+    // THEN
+    test.deepEqual(stack.resolve(widget.toJson()), [{
+      type: 'metric',
+      width: 6,
+      height: 6,
+      properties: {
+        view: 'timeSeries',
+        title: 'My live graph',
+        region: { Ref: 'AWS::Region' },
+        metrics: [
+          ['CDK', 'Test'],
+        ],
+        liveData: true,
+        yAxis: {},
+      },
+    }]);
+
+    test.done();
+  },
+
   'can use imported alarm with graph'(test: Test) {
     // GIVEN
     const stack = new Stack();