[v2.9] Virtual Resource filters (#288)

Adds logic which adds virtual fields resources. This allows these fields
to be sorted/filtered on when the SQL cache is enabled. Id and
metadata.state.name were added as the first two fields.

Co-authored-by: Michael Bolot <michael.bolot@suse.com>

pkg/resources/virtual/common/util.go

@@ -0,0 +1,40 @@
+package common
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/client-go/tools/cache"
+)
+
+// GetUnstructured retrieves an unstructured object from the provided input. If this is a signal
+// object (like cache.DeletedFinalStateUnknown), returns true, indicating that this wasn't an
+// unstructured object, but doesn't need to be processed by our transform function
+func getUnstructured(obj any) (*unstructured.Unstructured, bool, error) {
+	raw, ok := obj.(*unstructured.Unstructured)
+	if !ok {
+		_, isFinalUnknown := obj.(cache.DeletedFinalStateUnknown)
+		if isFinalUnknown {
+			// As documented in the TransformFunc interface
+			return nil, true, nil
+		}
+		return nil, false, fmt.Errorf("object was of type %T, not unstructured", raw)
+	}
+	return raw, false, nil
+}
+
+// toMap converts an object to a map[string]any which can be stored/retrieved from the cache. Currently
+// uses json encoding to take advantage of tag names
+func toMap(obj any) (map[string]any, error) {
+	bytes, err := json.Marshal(obj)
+	if err != nil {
+		return nil, fmt.Errorf("unable to marshal object: %w", err)
+	}
+	var retObj map[string]any
+	err = json.Unmarshal(bytes, &retObj)
+	if err != nil {
+		return nil, fmt.Errorf("unable to unmarshal object: %w", err)
+	}
+	return retObj, nil
+}