Fix kubernetes_node_taint so that taints are unique over key and effect and not just key

[xinkechen-evernorth]

Description

This PR seeks to fix the kubernetes_node_taint resource so that it's possible to set multiple effects for a given key. This is motivated by the fact that with kubectl it is possible to do the following:

❯ kubectl taint nodes dedicated-node.example.com key1=value:NoSchedule key1=value:NoExecute
node/dedicated-node.example.com tainted
❯ kubectl get node -o jsonpath='{.spec.taints}' dedicated-node.example.com
[{"effect":"NoSchedule","key":"key1","value":"value"},{"effect":"NoExecute","key":"key1","value":"value"}

A user attempting to express the same set of taints kubernetes_node_taint erroneously fails with the message that taints unique over key only.

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 ^TestAccKubernetesResourceNodeTaint"
...
=== RUN   TestAccKubernetesResourceNodeTaint_basic
--- PASS: TestAccKubernetesResourceNodeTaint_basic (8.44s)
=== RUN   TestAccKubernetesResourceNodeTaint_MultipleBasic
--- PASS: TestAccKubernetesResourceNodeTaint_MultipleBasic (21.67s)
=== RUN   TestAccKubernetesResourceNodeTaint_MultipleSameKeyDifferentEffect
--- PASS: TestAccKubernetesResourceNodeTaint_MultipleSameKeyDifferentEffect (8.80s)
=== RUN   TestAccKubernetesResourceNodeTaint_DuplicateTaintKeyAndEffectExpectError
--- PASS: TestAccKubernetesResourceNodeTaint_DuplicateTaintKeyAndEffectExpectError (1.86s)
PASS
ok  	github.com/hashicorp/terraform-provider-kubernetes/kubernetes	40.998s

Release Note

Release note for CHANGELOG:

`resource/kubernetes_node_taint`: Fix taint uniqueness check so it is enforced over key and effect and not solely key alone.

References

Documented examples of using the same key with a different effect

• Kubernetes PR that made taints unique by key and effect: make taints unique by <key, effect> on a node kubernetes/kubernetes#30590
• Kubernetes Documentation with example use case using the same key but different effect: https://kubernetes.io/docs/concepts/scheduling-eviction/taint-and-toleration/#example-use-cases

Community Note

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[xinkechen-evernorth]

Apologies for the ask since I know there is a sizeable queue, but is there an estimate on when an initial review might happen?

I want to make sure this PR is in a good spot before my personal availability becomes tied up for the next couple weeks and not have any requested changes or comments languish out here.