fix(custom-resources): incorrect IAM prefix generated for CloudWatch actions (#33078)

### Issue # (if applicable)

Closes #32968.

### Reason for this change

The mapping to look up the IAM prefix from a given service has a incorrect entry for Cloudwatch. It says Cloudwatch uses `monitoring` as the prefix but it is actually `cloudwatch` instead.

I cannot find any service that uses `monitoring` as prefix so I think it is safe to assume that nothing relies on the `monitoring` value. Therefore, there is no feature flag used in this PR.

### Description of changes

Updated the IAM prefix mapping.

### Describe any new or updated permissions being added

Updated the mapping to use correct IAM prefix.

### Description of how you validated changes

Updated unit tests to use AwsCustomResource with a Cloudwatch call.

Added integ test to use AwsCustomResource with a Cloudwatch call to tag an alarm and verify the tag is indeed added successfully.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: samson-keung

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@@ -827,7 +827,7 @@
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packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2/test/integ.alb.oidc.js.snapshot/asset.b98abee59e034ed29eeb601684dc34752baa86509a7d457d72305d4e19ecc80b.bundle/index.js renamed to packages/@aws-cdk-testing/framework-integ/test/aws-elasticloadbalancingv2-actions/test/integ.cognito.js.snapshot/asset.f692c9f68e4daba2abc99103efd3518bced1e9d7a2a89847b9b5d5473c64f1bd.bundle/index.js

@@ -903,7 +903,7 @@
      "S3Bucket": {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      },
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