Add meta.Duration as known type for diffing

So that this can be used for custom resources. The motivation for this
is issue argoproj#6008: with this change one should be able to use the known
type to ensure equal durations don't present a diff, e,g. via adding to
`argocd-cm`:

    data:
      resource.customizations.knownTypeFields.cert-manager.io_Certificate: |
        - field: spec.duration
          type: meta/v1/Duration

This change is based on 5b464c9, though
I've included the API version in the type path to be consistent with the
generated type (i.e. `meta/v1/Duration` and not `meta/Duration`).

For documentation I've just manually listed the extra types that aren't
auto-generated, though this requires having to keep this list and the
code in-sync but this is probably not a big issue since the number of
extra types is not frequently changed.

Signed-off-by: Matthew Hughes <matthewhughes934@gmail.com>

docs/user-guide/diffing.md

@@ -181,4 +181,7 @@ data:
       type: core/v1/PodSpec
 ```
 
-The list of supported Kubernetes types is available in [diffing_known_types.txt](https://raw.githubusercontent.com/argoproj/argo-cd/master/util/argo/normalizers/diffing_known_types.txt)
+The list of supported Kubernetes types is available in [diffing_known_types.txt](https://raw.githubusercontent.com/argoproj/argo-cd/master/util/argo/normalizers/diffing_known_types.txt) an additionally:
+
+* `core/Quantity`
+* `meta/v1/duration`

util/argo/normalizers/knowntypes_normalizer.go

@@ -8,6 +8,7 @@ import (
 	log "github.com/sirupsen/logrus"
 	v1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/resource"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 
@@ -32,6 +33,9 @@ func init() {
 	knownTypes["core/Quantity"] = func() interface{} {
 		return &resource.Quantity{}
 	}
+	knownTypes["meta/v1/Duration"] = func() interface{} {
+		return &metav1.Duration{}
+	}
 }
 
 // NewKnownTypesNormalizer create a normalizer that re-format custom resource fields using built-in Kubernetes types.

util/argo/normalizers/knowntypes_normalizer_test.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/argoproj/pkg/errors"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"sigs.k8s.io/yaml"
@@ -228,6 +229,32 @@ spec:
 	assert.Equal(t, "1250M", ram)
 }
 
+func TestNormalize_Duration(t *testing.T) {
+	rollout := mustUnmarshalYAML(`apiVersion: cert-manager.io/v1
+kind: Certificate
+metadata:
+  name: my-cert
+spec:
+  duration: 8760h
+`)
+	normalizer, err := NewKnownTypesNormalizer(map[string]v1alpha1.ResourceOverride{
+		"cert-manager.io/Certificate": {
+			KnownTypeFields: []v1alpha1.KnownTypeField{{
+				Type:  "meta/v1/Duration",
+				Field: "spec.duration",
+			}},
+		},
+	})
+	require.NoError(t, err)
+
+	require.NoError(t, normalizer.Normalize(rollout))
+
+	duration, ok, err := unstructured.NestedFieldNoCopy(rollout.Object, "spec", "duration")
+	require.NoError(t, err)
+	require.True(t, ok)
+	require.Equal(t, "8760h0m0s", duration)
+}
+
 func TestFieldDoesNotExist(t *testing.T) {
 	rollout := mustUnmarshalYAML(someCRDYaml)
 	normalizer, err := NewKnownTypesNormalizer(map[string]v1alpha1.ResourceOverride{