Add fallback decoder for unknown resources to handle CRDs

[janisz]

This PR adds a fallback when decoding unknown resources to be able to handle CRDs. The schema validation could be then performed with kubeconform check from #1033 and CEL from #1012. This should fix #606
It also deprecates the --fail-on-invalid-resource as it could be replaced by a new schema-validation check or kubeconform
This could be considered as breaking change as it changes the semantic of --fail-on-invalid-resource to fail on invalid yamls instead of failing on unknown objects or not matching schema but this could be mitigated by kubeconform.

Changes:

• Modified parseObjects to use unstructured decoder as fallback for unknown resource types
• Added comprehensive test suite covering standard K8s resources and CRDs
• Maintained backward compatibility for existing decode error handling
• Added test cases for Tekton Task CRD and other custom resources

The fallback allows kube-linter to parse CRDs like Tekton Pipelines without
failing, while delegating proper schema validation to specialized templates
like kubeconform and CEL expressions.

Fixes:

• [BUG] failed to decode: no kind "Pipeline" is registered for version "tekton.dev/v1beta1" #606
• Support CRDs #24
• Istio Checks #208

Refs:

• [FEATURE_REQUEST] Argo Rollouts support #848

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]

[janisz]

Tested by rebasing #1033 on this PR and running test from e2e but with flag

# ./kube-linter lint tests/checks/kubeconform.yml --fail-on-invalid-resource --do-not-auto-add-defaults --config e2etests/testdata/kubeconform-config.yaml
KubeLinter development

./tests/checks/kubeconform.yml: (object: default/invalid-daemonset apps/v1, Kind=DaemonSet) resource is not valid: problem validating schema. Check JSON formatting: jsonschema validation failed with 'https://raw.githubusercontent.com/yannh/kubernetes-json-schema/master/master-standalone-strict/daemonset-apps-v1.json#' - at '/spec': additional properties 'replicas' not allowed (check: kubeconform-validation, remediation: Fix the resource to conform to the Kubernetes API schema)

./tests/checks/kubeconform.yml: (object: default/invalid-pod /v1, Kind=Pod) resource is not valid: problem validating schema. Check JSON formatting: jsonschema validation failed with 'https://raw.githubusercontent.com/yannh/kubernetes-json-schema/master/master-standalone-strict/pod-v1.json#' - at '/spec': additional properties 'invalidField' not allowed (check: kubeconform-validation, remediation: Fix the resource to conform to the Kubernetes API schema)

- ./tests/checks/kubeconform.yml: (object: <no namespace>/ /, Kind=) failed to decode: no kind "CustomResource" is registered for version "example.com/v1" in scheme "pkg/runtime/scheme.go:110" (check: failed-to-load-object, remediation: Confirm that the file is accessible and is valid k8s yaml.)

- Error: found 3 lint errors
+ Error: found 2 lint errors

[janisz]

This change is part of the following stack:

• Add kubeconform template for schema validation #1033
  • Add fallback decoder for unknown resources to handle CRDs #1037 ◀

_{Change managed by git-spice.}