feat(custom): handle cross-account/cross-region search expressions fo…

…r dashboards (#551)

Building on top of #533, but `monitorCustom` has its own API for
simplifying search expression queries so we need to explicitly handle
it.

Regular `new Metric(...)` calls just pass in the `account`/`metric` via
that API.

---

_By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license_

lib/monitoring/custom/CustomMonitoring.ts

@@ -127,6 +127,22 @@ export interface CustomMetricSearch {
    * default: AxisPosition.LEFT
    */
   readonly position?: AxisPosition;
+
+  /**
+   * Account which this metric comes from.
+   * Note that alarms cannot be created for cross-account metrics.
+   *
+   * @default - Deployment account.
+   */
+  readonly account?: string;
+
+  /**
+   * Region which this metric comes from.
+   * Note that alarms cannot be created for cross-region metrics.
+   *
+   * @default - Deployment region.
+   */
+  readonly region?: string;
 }
 
 /**
@@ -482,6 +498,8 @@ export class CustomMonitoring extends Monitoring {
           metric.namespace,
           metric.label,
           metric.period,
+          metric.region,
+          metric.account,
         );
       } else {
         // general metric

test/monitoring/custom/CustomMonitoring.test.ts

@@ -44,7 +44,13 @@ test("snapshot test", () => {
           // regular metric
           new Metric({ metricName: "DummyMetric1", namespace, dimensionsMap }),
           // metric with alarm
-          new Metric({ metricName: "DummyMetric2", namespace, dimensionsMap }),
+          new Metric({
+            metricName: "DummyMetric2",
+            namespace,
+            dimensionsMap,
+            account: "01234567890",
+            region: "us-west-2",
+          }),
           {
             metric: new Metric({
               metricName: "DummyMetric3",
@@ -71,6 +77,14 @@ test("snapshot test", () => {
             dimensionsMap,
             statistic: MetricStatistic.SUM,
           },
+          {
+            searchQuery: "DummyMetric5-",
+            namespace,
+            dimensionsMap,
+            statistic: MetricStatistic.SUM,
+            account: "01234567890",
+            region: "us-west-2",
+          },
         ],
       },
       {