Merge pull request #61905 from mengqiy/mergePatchesInSMP

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

add a func to merge multiple Strategic Merge Patches into one patch

This PR is adding a function similar to 9fa11df836/merge.go (L95-L100)
It merges multiple SMPs and yield another SMP.

This PR has no risk to existing SMP code.

```release-note
NONE
```
/cc @apelisse
/assign @pwittrock

staging/src/k8s.io/apimachinery/pkg/util/strategicpatch/patch.go

@@ -880,6 +880,29 @@ func StrategicMergeMapPatchUsingLookupPatchMeta(original, patch JSONMap, schema
 	return mergeMap(original, patch, schema, mergeOptions)
 }
 
+// MergeStrategicMergeMapPatchUsingLookupPatchMeta merges strategic merge
+// patches retaining `null` fields and parallel lists. If 2 patches change the
+// same fields and the latter one will override the former one. If you don't
+// want that happen, you need to run func MergingMapsHaveConflicts before
+// merging these patches. Applying the resulting merged merge patch to a JSONMap
+// yields the same as merging each strategic merge patch to the JSONMap in
+// succession.
+func MergeStrategicMergeMapPatchUsingLookupPatchMeta(schema LookupPatchMeta, patches ...JSONMap) (JSONMap, error) {
+	mergeOptions := MergeOptions{
+		MergeParallelList:    false,
+		IgnoreUnmatchedNulls: false,
+	}
+	merged := JSONMap{}
+	var err error
+	for _, patch := range patches {
+		merged, err = mergeMap(merged, patch, schema, mergeOptions)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return merged, nil
+}
+
 // handleDirectiveInMergeMap handles the patch directive when merging 2 maps.
 func handleDirectiveInMergeMap(directive interface{}, patch map[string]interface{}) (map[string]interface{}, error) {
 	if directive == replaceDirective {