Support custom nested fields that have path that contains types other than struct (#538)

Issue #, if available:

Description of changes:

Say we want to overwrite a nested field type e.g. for `WAFv2` controller (this is needed due to a cyclic dependency):
```
resources:
  RuleGroup:
      Rules.Statement.AndStatement:
        type: string
```

Currently, the [overwrite code logic](https://github.com/aws-controllers-k8s/code-generator/blob/62466746500d0c01fcfa8e8e3ca6abd9386e4687/pkg/model/crd.go#L660-L687) does not work for the above scenario and it returns the following error:
```
Expected parent field to be of type structure, but found list
```

This happens because `Rules` is not of type `struct`, but `[]struct`, and the referenced code logic requires that all fields within the path (i.e. `Rules` and `Statement` to be of type `struct`).

This PR relaxes the logic to allow fields within the path to also be of types `[]struct` and `map[]struct`.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: TiberiuGC

pkg/model/crd.go

@@ -656,17 +656,23 @@ func (crd *CRD) addCustomNestedFields(customNestedFields map[string]*ackgenconfi
 		topLevelField := fieldParts[0]
 
 		f, ok := crd.checkSpecOrStatus(topLevelField)
-
-		if ok && f.ShapeRef.Shape.Type != "structure" {
-			// We need to panic here because the user is providing wrong configuration.
-			msg := fmt.Sprintf("Expected parent field to be of type structure, but found %s", f.ShapeRef.Shape.Type)
+		if !ok {
+			msg := fmt.Sprintf("Expected top level field %s to be present in Spec or Status", topLevelField)
 			panic(msg)
 		}
 
-		// If the provided top level field is not in the crd.SpecFields or crd.StatusFields...
-		if !ok {
-			// We need to panic here because the user is providing wrong configuration.
-			msg := fmt.Sprintf("Expected top level field %s to be present in Spec or Status", topLevelField)
+		shape := f.ShapeRef.Shape
+		isValidShapeType := func(shape *awssdkmodel.Shape) bool {
+			if shape.Type == "structure" ||
+				(shape.Type == "list" && shape.MemberRef.Shape.Type == "structure") ||
+				(shape.Type == "map" && shape.ValueRef.Shape.Type == "structure") {
+				return true
+			}
+			return false
+		}
+
+		if !isValidShapeType(shape) {
+			msg := fmt.Sprintf("Expected top level field %s to be of type structure, []structure or map[]structure, but found %s", topLevelField, shape.Type)
 			panic(msg)
 		}
 
@@ -676,13 +682,20 @@ func (crd *CRD) addCustomNestedFields(customNestedFields map[string]*ackgenconfi
 
 		// loop over the all left fieldParts except the last one
 		for _, currentFieldName := range fieldParts[1 : len(fieldParts)-1] {
-			// Check if parentField contains current field
 			currentField, ok := parentField.MemberFields[currentFieldName]
-			if !ok || currentField.ShapeRef.Shape.Type != "structure" {
-				// Check if the field exists AND is of type structure
-				msg := fmt.Sprintf("Cannot inject field, %s member doesn't exist or isn't a structure", currentFieldName)
+			shape := currentField.ShapeRef.Shape
+
+			// if the parentField doesn't contain the current field
+			if !ok {
+				msg := fmt.Sprintf("Cannot inject field, nested field %s doesn't exist", currentFieldName)
 				panic(msg)
 			}
+
+			if !isValidShapeType(shape) {
+				msg := fmt.Sprintf("Expected nested field %s to be of type structure, []structure or map[]structure, but found %s", currentFieldName, shape.Type)
+				panic(msg)
+			}
+
 			parentField = currentField
 		}