Annotate TargetPath and OutputImageDir with omitempty

This omits them from YAML output if the value isn't specified. Before
this change, YAMLs would print `outputImageDir: ""` if it was
unspecified.

pkg/apis/pipeline/v1alpha1/task_types.go

@@ -122,10 +122,10 @@ type TaskResource struct {
  // TargetPath is the path in workspace directory where the task resource
  // will be copied.
  // +optional
- TargetPath string `json:"targetPath"`
+ TargetPath string `json:"targetPath,omitempty"`
  // Path to the index.json file for output container images.
  // +optional
- OutputImageDir string `json:"outputImageDir"`
+ OutputImageDir string `json:"outputImageDir,omitempty"`
 }
 
 // Outputs allow a task to declare what data the Build/Task will be producing,