[Mics]: support mulit metrics for podautoscaler

[googs1025]

Pull Request Description

[Please provide a clear and concise description of your changes here]

Related Issues

Resolves: #[Insert issue number(s)]

fix: #1591

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[gemini-code-assist]

Summary of Changes

Hello @googs1025, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the PodAutoscaler's capabilities by introducing support for multiple metrics. This allows for more sophisticated and robust autoscaling decisions, as the system can now consider various performance indicators simultaneously. The core scaling algorithms and internal context management have been adapted to accommodate this change, ensuring that the autoscaler can effectively respond to diverse workload demands by scaling based on the most critical metric at any given time.

Highlights

• Multi-Metric Support: The PodAutoscaler now supports defining multiple metrics for scaling. The system will calculate desired replicas for each configured metric and then apply the maximum of these recommendations.
• Algorithm Updates: Both the APA (Adaptive Pod Autoscaler) and KPA (Knative Pod Autoscaler) algorithms have been updated to accept a specific metric name when computing target replicas, allowing them to retrieve the correct target value from the scaling context.
• Scaling Context Refactoring: The internal ScalingContext has been refactored to store metric-specific target values in a map (MetricTargets) keyed by metric name, replacing the previous single TargetValue and ScalingMetric fields.
• Validation Logic Enhanced: The validation logic for PodAutoscaler resources has been updated to correctly handle and validate multiple metricsSources defined in the spec.
• New Sample Configuration: A new sample YAML file (multimetrics-apa.yaml) has been added to demonstrate how to configure a PodAutoscaler to use multiple metrics for scaling.

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[gemini-code-assist]

Code Review

This pull request introduces support for multiple metrics in the PodAutoscaler, a significant enhancement. The core logic is updated to iterate through all specified metric sources, compute a scaling recommendation for each, and then select the maximum desired replica count. This ensures the system scales up to meet the demand of the most constrained resource. The changes are well-structured, touching the autoscaler, context, and validation logic, and are accompanied by updated tests and a new sample YAML for multi-metric configuration. My review identified one bug in the implementation where the scaling reason and algorithm were not correctly propagated when using multiple metrics. I've provided a code suggestion to address this. Overall, this is a great improvement to the autoscaler's flexibility.

[googs1025]

remove this func

[googs1025]

note: Do we need to limit the number of metricsSources slices at the api level?

[Jeffwan]

Do we need to limit the number of metricsSources slices at the api level?

I think we do not need to limit it at this moment.