docs/aws_appautoscaling_policy: link AWS API reference for predictive metric types

Address review feedback from @justinretzolk on PR #47641: enum values
change over time, so link to the canonical AWS API reference for each
of the three predictive scaling metric specifications instead of
hard-coding the list of valid values inline.

The note that resource_label is required for ALB-based metric types is
retained but no longer parenthetically lists the specific ALB values,
since those are also documented at the linked references.

Author: alien2003

website/docs/r/appautoscaling_policy.html.markdown

@@ -297,22 +297,22 @@ The `predictive_scaling_policy_configuration` `metric_specification` `customized
 
 The `predictive_scaling_policy_configuration` `metric_specification` `predefined_load_metric_specification` configuration block supports the following arguments:
 
-* `predefined_metric_type` - (Required) Predefined load metric type. Valid values are `ECSServiceAverageCPUUtilization`, `ECSServiceAverageMemoryUtilization`, `ECSServiceCPUUtilization`, `ECSServiceMemoryUtilization`, `ECSServiceTotalCPUUtilization`, `ECSServiceTotalMemoryUtilization`, `ALBRequestCount`, `ALBRequestCountPerTarget`, and `TotalALBRequestCount`.
-* `resource_label` - (Optional) Label that uniquely identifies a target group. Required when `predefined_metric_type` is one of the ALB-based values (`ALBRequestCount`, `ALBRequestCountPerTarget`, `TotalALBRequestCount`).
+* `predefined_metric_type` - (Required) Predefined load metric type. See the [`PredictiveScalingPredefinedLoadMetricSpecification`](https://docs.aws.amazon.com/autoscaling/application/APIReference/API_PredictiveScalingPredefinedLoadMetricSpecification.html) AWS API reference for valid values.
+* `resource_label` - (Optional) Label that uniquely identifies a target group. Required when `predefined_metric_type` is an ALB-based value.
 
 ### predictive_scaling_policy_configuration metric_specification predefined_metric_pair_specification
 
 The `predictive_scaling_policy_configuration` `metric_specification` `predefined_metric_pair_specification` configuration block supports the following arguments:
 
-* `predefined_metric_type` - (Required) Pair of predefined metrics (one load metric and one scaling metric) to use. Valid values are `ECSServiceAverageCPUUtilization`, `ECSServiceAverageMemoryUtilization`, `ECSServiceCPUUtilization`, `ECSServiceMemoryUtilization`, `ECSServiceTotalCPUUtilization`, `ECSServiceTotalMemoryUtilization`, `ALBRequestCount`, `ALBRequestCountPerTarget`, and `TotalALBRequestCount`.
-* `resource_label` - (Optional) Label that uniquely identifies a specific target group from which to determine the total and average request count. Required when `predefined_metric_type` is one of the ALB-based values (`ALBRequestCount`, `ALBRequestCountPerTarget`, `TotalALBRequestCount`).
+* `predefined_metric_type` - (Required) Pair of predefined metrics (one load metric and one scaling metric) to use. See the [`PredictiveScalingPredefinedMetricPairSpecification`](https://docs.aws.amazon.com/autoscaling/application/APIReference/API_PredictiveScalingPredefinedMetricPairSpecification.html) AWS API reference for valid values.
+* `resource_label` - (Optional) Label that uniquely identifies a specific target group from which to determine the total and average request count. Required when `predefined_metric_type` is an ALB-based value.
 
 ### predictive_scaling_policy_configuration metric_specification predefined_scaling_metric_specification
 
 The `predictive_scaling_policy_configuration` `metric_specification` `predefined_scaling_metric_specification` configuration block supports the following arguments:
 
-* `predefined_metric_type` - (Required) Predefined scaling metric type. Valid values are `ECSServiceAverageCPUUtilization`, `ECSServiceAverageMemoryUtilization`, `ECSServiceCPUUtilization`, `ECSServiceMemoryUtilization`, `ECSServiceTotalCPUUtilization`, `ECSServiceTotalMemoryUtilization`, `ALBRequestCount`, `ALBRequestCountPerTarget`, and `TotalALBRequestCount`.
-* `resource_label` - (Optional) Label that uniquely identifies a specific target group from which to determine the average request count. Required when `predefined_metric_type` is one of the ALB-based values (`ALBRequestCount`, `ALBRequestCountPerTarget`, `TotalALBRequestCount`).
+* `predefined_metric_type` - (Required) Predefined scaling metric type. See the [`PredictiveScalingPredefinedScalingMetricSpecification`](https://docs.aws.amazon.com/autoscaling/application/APIReference/API_PredictiveScalingPredefinedScalingMetricSpecification.html) AWS API reference for valid values.
+* `resource_label` - (Optional) Label that uniquely identifies a specific target group from which to determine the average request count. Required when `predefined_metric_type` is an ALB-based value.
 
 ### step_scaling_policy_configuration