feat(kinesisanalytics-flink): Add metrics to Flink applications (#19599)

I PR'd the [original version of the aws-kinesisanalytics-flink constructs](#12464) to CDK. I'm following up to add the missing `metric*` methods according to the [design guidelines](https://github.com/aws/aws-cdk/blob/master/docs/DESIGN_GUIDELINES.md#metrics).

[Reference for Flink Application metrics](https://docs.aws.amazon.com/kinesisanalytics/latest/java/metrics-dimensions.html). I have a few running Flink apps and I was able to see that KPUs are also reported for the Flink apps.

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### All Submissions:

* [x] Have you followed the guidelines in our [Contributing guide?](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md)
  * [x] I don't think conventional metric changes require an update to the README.

### New Features

* [x] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [x] Did you use `cdk-integ` to deploy the infrastructure and generate the snapshot (i.e. `cdk-integ` without `--dry-run`)?

*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-kinesisanalytics-flink/README.md

@@ -18,7 +18,7 @@
 This package provides constructs for creating Kinesis Analytics Flink
 applications. To learn more about using using managed Flink applications, see
 the [AWS developer
-guide](https://docs.aws.amazon.com/kinesisanalytics/latest/java/what-is.html).
+guide](https://docs.aws.amazon.com/kinesisanalytics/latest/java/).
 
 ## Creating Flink Applications