Add tests to k8sutil (#296)

Adds more unit tests to sections that are easy to test.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Tests**
* Added unit tests for Kubernetes owner-reference and finalizer helper
functions to ensure correct behavior.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

internal/k8sutil/finalizer_test.go

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
+package k8sutil
+
+import (
+	"testing"
+
+	"github.com/go-openapi/testify/v2/require"
+)
+
+func TestFinalizer(t *testing.T) {
+	t.Parallel()
+
+	res := Finalizer("foo")
+	require.Equal(t, "finalizers.netbird.io/foo", res)
+}