Create sub-structure for Metric rendering options

This allows to create custom graphs easier by creating sub-class of
metric and overriding the `toGraphConfig` method. Before attributes have
been only selectively copied to the widget configuration.

```
class HiddenMetric extends Metric {
  public toGraphConfig(): any {
    const ret = super.toGraphConfig();
    ret.renderingProperties.visible = false;
  }
}
```

Before `visible` would not have been taken over since it was not part of
options.

Docs: https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/CloudWatch-Dashboard-Body-Structure.html#CloudWatch-Dashboard-Properties-Rendering-Object-Format

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

@@ -312,13 +312,7 @@ function metricJson(metric: IMetric, yAxis: string): any[] {
   }
 
   // Options
-  ret.push({
-    yAxis,
-    label: config.label,
-    color: config.color,
-    period: config.period,
-    stat: config.statistic,
-  });
+  ret.push({ yAxis, ...config.renderingProperties });
 
   return ret;
 }

packages/@aws-cdk/aws-cloudwatch/lib/metric-types.ts

@@ -132,6 +132,16 @@ export interface MetricGraphConfig {
    */
   readonly metricName: string;
 
+  /**
+   * Rendering properties override yAxis parameter of the widget object
+   */
+  readonly renderingProperties: MetricRenderingProperties;
+}
+
+/**
+ * Custom rendering properties that override the default rendering properties specified in the yAxis parameter of the widget object.
+ */
+export interface MetricRenderingProperties {
   /**
    * How many seconds to aggregate over
    */
@@ -150,10 +160,5 @@ export interface MetricGraphConfig {
   /**
    * Aggregation function to use (can be either simple or a percentile)
    */
-  readonly statistic?: string;
-
-  /**
-   * The unit of the alarm
-   */
-  readonly unit?: Unit;
-}
+  readonly stat?: string;
+}

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

@@ -195,11 +195,12 @@ export class Metric implements IMetric {
       dimensions: this.dimensionsAsList(),
       namespace: this.namespace,
       metricName: this.metricName,
-      period: this.period.toSeconds(),
-      statistic: this.statistic,
-      unit: this.unit,
-      color: this.color,
-      label: this.label,
+      renderingProperties: {
+        period: this.period.toSeconds(),
+        stat: this.statistic,
+        color: this.color,
+        label: this.label,
+      },
     };
   }
 

packages/@aws-cdk/aws-cloudwatch/package.json

@@ -81,7 +81,7 @@
   "awslint": {
     "exclude": [
       "duration-prop-type:@aws-cdk/aws-cloudwatch.MetricAlarmConfig.period",
-      "duration-prop-type:@aws-cdk/aws-cloudwatch.MetricGraphConfig.period"
+      "duration-prop-type:@aws-cdk/aws-cloudwatch.MetricRenderingProperties.period"
     ]
   },
   "engines": {