fix SpreadConstraint json tag issue in policy API (#46)

Signed-off-by: Kevin Wang <kevinwzf0126@gmail.com>

artifacts/deploy/propagationstrategy.karmada.io_propagationpolicies.yaml

@@ -197,11 +197,11 @@ spec:
                       description: SpreadConstraint represents the spread constraints
                         on resources.
                       properties:
-                        maximumClusters:
+                        maximum:
                           description: Maximum restricts the maximum number of cluster
                             units to be selected.
                           type: integer
-                        minimumClusters:
+                        minimum:
                           description: Minimum restricts the minimum number of cluster
                             units to be selected.
                           type: integer

artifacts/example/simple_policy.yaml

@@ -22,6 +22,6 @@ spec:
       exclude:
         - cluster2
     spreadConstraints:
-      - maximumClusters: 3
-        minimumClusters: 3
-  schedulerName: default
+      - maximum: 3
+        minimum: 3
+  schedulerName: default

pkg/apis/propagationstrategy/v1alpha1/propagation_types.go

@@ -105,11 +105,11 @@ type SpreadConstraint struct {
 
 	// Maximum restricts the maximum number of cluster units to be selected.
 	// +optional
-	Maximum int `json:"maximumClusters,omitempty"`
+	Maximum int `json:"maximum,omitempty"`
 
 	// Minimum restricts the minimum number of cluster units to be selected.
 	// +optional
-	Minimum int `json:"minimumClusters,omitempty"`
+	Minimum int `json:"minimum,omitempty"`
 }
 
 // ClusterAffinity represents the filter to select clusters.