Fix deletion not found handling in the delete operation and adding related tests

[JaylonmcShan03]

Description

Fixes #2188
This PR introduces changes to handle "404 Not Found" errors during the deletion of Kubernetes resources, particularly in cases where the resource may have already been deleted by an operator managing the CRD before Terraform attempts to delete it.

Changes Introduced:

Added logic to check for IsNotFound(err) when calling Delete on resources.

If a "404 Not Found" error is encountered, it is now treated as a successful deletion and logged as "Resource
already deleted, ignoring 404 error".
Other errors during deletion will continue to be handled as before.

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=TestAccXXX'
jaylon.mcshan@jaylon terraform-provider-kubernetes % go test -v -tags=acceptance ./manifest/test/acceptance -run TestKubernetesManifest_DeletionNotFound

2024/09/25 09:53:50 Testing against Kubernetes API version: v1.30.0
=== RUN   TestKubernetesManifest_DeletionNotFound
    delete_not_found_test.go:35: Verifying if namespace tf-acc-test-vkxthtphka exists
    delete_not_found_test.go:54: Applying Terraform configuration to create ConfigMap
    delete_not_found_test.go:64: Terraform state: &{false 1.0 1.8.3 0x14000b787d0 []}
    delete_not_found_test.go:68: Checking if ConfigMap tf-acc-test-bypcuockzy in namespace tf-acc-test-vkxthtphka was created
2024-09-25T09:53:52.894-0500 [WARN]  sdk.proto: Response contains warning diagnostic: tf_rpc=ApplyResourceChange diagnostic_detail="The resource \"tf-acc-test-bypcuockzy\" was not found in the Kubernetes API. This may be due to the resource being already deleted." diagnostic_severity=WARNING diagnostic_summary="Resource \"tf-acc-test-bypcuockzy\" was already deleted" tf_resource_type=kubernetes_manifest tf_proto_version=5.6 tf_provider_addr=registry.terraform.io/hashicorp/kubernetes tf_req_id=1b6b3752-6308-e766-046e-1e392d2e3bcf
--- PASS: TestKubernetesManifest_DeletionNotFound (2.63s)
PASS
ok      github.com/hashicorp/terraform-provider-kubernetes/manifest/test/acceptance     3.421s
...

Release Note

Release note for CHANGELOG:

...
handling "404 Not Found" errors during the deletion of Kubernetes resources, particularly in cases where the resource may have already been deleted by an operator managing the CRD before Terraform attempts to delete it.

References

Community Note

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[alexsomesan]

I would add a reference to the manifest resource here, to make it clear this change only affects its behaviour.

Suggested change

	handling "404 Not Found" errors during the deletion of Kubernetes resources, particularly in cases where the resource may have already been deleted by an operator managing the CRD before Terraform attempts to delete it.
	`kubernetes_manifest` - handling "404 Not Found" errors during the deletion of Kubernetes resources, particularly in cases where the resource may have already been deleted by an operator managing the CRD before Terraform attempts to delete it.

[alexsomesan]

I think this return line needs to go outside of the else block.

[alexsomesan]

Looks good, only a couple of small tidy-ups needed. See my comments above.

[alexsomesan]

Looks great, @JaylonmcShan03!
Thanks for taking care of this issue!