feat(cloudwatch): period in GraphWidget

[bentonkribbs]

This PR adds support for the period property in CloudWatch GraphWidgets.

The property in question can be seen here, under "period": https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/CloudWatch-Dashboard-Body-Structure.html#CloudWatch-Dashboard-Properties-Metric-Widget-Object

This fixes #6367

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[gitpod-io]

[aws-cdk-automation]

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[rix0rrr]

I think doing this will break how metrics are rendered. Right now, when metrics render themselves they will render their own period if it is != 300, assuming that the graph period is going to be 5 minutes (and so no need to render duplicate numbers).

With this change, if you set the graph period to 1 minute and add a 5 minute metric, the metric will NOT RENDER its period and hence appear at a 1 minute rate (which is counter to what you were expecting).

Can you describe the problem you are solving? We may need to do something else/more other than just forward a property to the user.

[NetaNir]

see Rico's comment

[bentonkribbs]

My primary use case was creating a GraphWidget with a MathExpression, and trying to set all MathExpressions and Metrics in this GraphWidget to use a period of 60 seconds. At the time, the MathExpression's period wasn't working as expected in our local version of CDK, but this: ( #13078) now solves my use case.

I am not sure if there is an other use case where the GraphWidget's period property would need set which can't be satisfied by setting the individual MathExpressions and Metrics periods. Based on the fact that IMetric is only implemented by these two classes, I think this PR is no longer needed.