Fix metrics hpa diffbug

[BBBmau]

Description

This PR changes the attribute type of metrics in horizontal pod autoscaler to Set in order to prevent Diffs from appearing despite their not being any change in the tfconfig. (Diff comes from out of order metrics list, using a set type for metrics would prevent this.)

Fixes #1188

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc TESTARGS="-run TestAccKubernetesHorizontalPodAutoscalerV2Beta2_basic"

...

Release Note

Release note for CHANGELOG:

`kubernetes/resource_horizontal_pod_autoscaler.go`: Change Lists to Set in metrics to prevent out of order metrics Diff

References

Community Note

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[BBBmau]

I'll need some advice on how to handle a bug when changing from Lists to Sets

It looks to solve the problem however I noticed that when attempting to patch the resource, it produces an empty metric value in the set. Resulting in

 Error: Failed to update horizontal pod autoscaler: HorizontalPodAutoscaler.autoscaling "my-app-hpa" is invalid: [spec.metrics[0].type: Required value: must specify a metric source type, spec.metrics[0].type: Unsupported value: "": supported values: "ContainerResource", "External", "Object", "Pods", "Resource"]

due to their being an empty metric block being added to the set despite not their being one in the config. This can be seen when applying the configs from TestAccKubernetesHorizontalPodAutoscalerV2Beta2_basic

1. Running basic config
2. Running modified config

will result in the Error.

I'm not sure where exactly the empty metric block is being added in the Update function. I'll need some input on this. @jrhouston @alexsomesan

[BBBmau]

This is currently Blocked after discussing this issue further with @alexsomesan. We discovered that the extra empty metric value comes from d.Get("metrics").(*Schema.Set) which comes from the terraform-plugin-sdk repo. I'll be making an issue in that repo bringing up the block that I'm facing for fixing the metrics HPA Diff Bug

[jrhouston]

Instead of changing the type here, couldn't we just use a DiffSuppressFunc on this attribute, sort the old and new values and if they're the same then suppress the diff?