refactor(crd): move CR from openebs.io to zfs.openebs.io (#70)

Changed the group name from openebs.io to zfs.openebs.io.

Now ZFS Volume CR will look like this : 
```
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: zfszvolumes.zfs.openebs.io
spec:
  group: zfs.openebs.io
  version: v1alpha1
  scope: Namespaced
  names:
    plural: zfsvolumes
    singular: zfsvolume
    kind:ZFSVolume
    shortNames:
    - zfsvol
    - zv
```

Snapshot CR will look like this :
```
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: zfssnapshots.zfs.openebs.io
spec:
  group: zfs.openebs.io
  version: v1alpha1
  scope: Namespaced
  names:
    plural: fssnapshots
    singular: zfssnapshot
    kind: ZFSSnapshot
    shortNames:
    - zfssnapshot
    - zfssnap

```


Signed-off-by: Pawan <pawan@mayadata.io>

pkg/apis/openebs.io/zfs/v1alpha1/register.go

@@ -28,7 +28,7 @@ import (
 // NOTE:
 //  This variable name should not be changed
 var SchemeGroupVersion = schema.GroupVersion{
-	Group:   "openebs.io",
+	Group:   "zfs.openebs.io",
 	Version: "v1alpha1",
 }