cloudwatch: support bands in horizontal and vertical annotations

[humanzz]

Describe the feature

Horizontal and Vertical annotations support declaring a band (from, to) as can be seen in Horizontal Annotations and Vertical Annotations sections in https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/CloudWatch-Dashboard-Body-Structure.html

The current implementation assumes just a single value with an above/below before/after shading

• https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-cloudwatch/lib/graph.ts#L721
• https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-cloudwatch/lib/graph.ts#L760

Use Case

Showing bands in metrics widgets, and coloring cells in the yet-to-be-implemented table widget #28975

Proposed Solution

A likely nice implementation would've been to change HorizontalAnnotation and VerticalAnnotation to classes with factory methods and a toJson or render method.

This, however, would be a breaking change.

As such, I'm not sure what the best approach would be, I can think of some options

1. Update the interfaces to have an additional field that captures the label and value of the other point in the range. This, however, will require widgets to check for that field, and render accordingly.
2. introduce new classes, new props fields, to replace the existing ones while marking them as deprecated. The challenge with this would be in naming those classes/fields as the good names are already taken

Other Information

I might be able to contribute a change, if discussions here lead to an agreed on approach

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

2.125.0

Environment details (OS name and version, etc.)

macOS

[humanzz]

Having been working on #28975, I actually ended up introducing a new Threshold class for the new TableWidget in #29078.

This class is a long the lines of having new classes for HorizontalAnnotation and VerticalAnnotation

[pahud]

Thanks for the use case sharing and proposed solutions. We welcome and appreciate any PRs for this.