fix: patch additions honor source key style

When a patch appends a new node, it should honor the key style from the
patch. Prior to this commit, no style was applied, leading to problems
when the key value could be interpreted as a different type based on its
content. For example, "9110" needs quoting to ensure it is seen as a
string in yaml.

kyaml/yaml/fns.go

@@ -690,6 +690,10 @@ type FieldSetter struct {
 	// when setting it.  Otherwise, if an existing node is found, the style is
 	// retained.
 	OverrideStyle bool `yaml:"overrideStyle,omitempty"`
+
+	// AppendKeyStyle defines the style of the key when no existing node is
+	// found, and a new node is appended.
+	AppendKeyStyle Style `yaml:"appendKeyStyle,omitempty"`
 }
 
 func (s FieldSetter) Filter(rn *RNode) (*RNode, error) {
@@ -747,6 +751,7 @@ func (s FieldSetter) Filter(rn *RNode) (*RNode, error) {
 		&yaml.Node{
 			Kind:        yaml.ScalarNode,
 			Value:       s.Name,
+			Style:       s.AppendKeyStyle,
 			HeadComment: s.Comments.HeadComment,
 			LineComment: s.Comments.LineComment,
 			FootComment: s.Comments.FootComment,