fix: Add missing CRD to the `crds` directory (#235)

Why
---
The Helm chart wasn't installing the `workflow-template` CRD.

charts/argo/Chart.yaml

@@ -2,7 +2,7 @@ apiVersion: v1
 appVersion: "v2.4.3"
 description: A Helm chart for Argo Workflows
 name: argo
-version: 0.6.6
+version: 0.6.7
 icon: https://raw.githubusercontent.com/argoproj/argo/master/docs/assets/argo.png
 home: https://github.com/argoproj/argo-helm
 maintainers:

charts/argo/crds/workflow-template-crd.yaml

@@ -0,0 +1,16 @@
+apiVersion: apiextensions.k8s.io/v1beta1
+kind: CustomResourceDefinition
+metadata:
+  name: workflowtemplates.argoproj.io
+  annotations:
+    helm.sh/hook: crd-install
+    helm.sh/hook-delete-policy: before-hook-creation
+spec:
+  group: argoproj.io
+  version: v1alpha1
+  scope: Namespaced
+  names:
+    kind: WorkflowTemplate
+    plural: workflowtemplates
+    shortNames:
+    - wftmpl