(autoscaling): step scaling policy max steps not validated correctly

[scanlonp]

Describe the bug

#26215 asked for validation on the max number of steps in a step scaling policy. @jedkass noted that certain policies over 20 steps fail deployment (#26215 (comment)).

Expected Behavior

Invalid number of steps in a policy fails at synth time rather than deploy time.

Current Behavior

Calling a private method like below where scalableTaskCount was created on a FargateService object:

defineAutoScaleDownPolicy(scalableTaskCount: ScalableTaskCount) {
    const minTaskCount = this.someConfig.minTaskCount;
    const maxTaskCount = this.someConfig.maxTaskCount;
    const scalingSteps = [];
    for (let lowerThreshold = 10; maxTaskCount - lowerThreshold > minTaskCount; lowerThreshold += 10) {
      scalingSteps.push({
        lower: lowerThreshold,
        change: -lowerThreshold + 10,
      });
    }

    scalableTaskCount.scaleOnMetric(`some-unique-id`, {
      metric: myMetric,
      adjustmentType: AdjustmentType.CHANGE_IN_CAPACITY,
      scalingSteps: scalingSteps,
    });
  }
}

minTaskCount is 40 and maxTaskCount is 267, which results in scalingSteps.length == 22

This fails to deploy with

There can be at most 20 step adjustments per scaling policy (Service: AWSApplicationAutoScaling; Status Code: 400; Error Code: ValidationException, etc...

Reproduction Steps

See current behavior.

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.94.0

Framework Version

No response

Node.js Version

18

OS

Mac

Language

Typescript

Language Version

No response

Other information

No response