Overlay onboarding for Add Link & Add Image tasks share the same dialog and buttons. The only differences are the panel content and the logger class used. AddLinkOnboardingDialog class should be generalized to StructuredTaskOnboardingDialog.
Additionally, message keys (and their qqqs) for the dialog controls should be renamed to reflect this as well.
| Old key name | New key name |
| growthexperiments-addlink-onboarding-dialog-progress | growthexperiments-structuredtask-onboarding-dialog-progress |
| growthexperiments-addlink-onboarding-dialog-title | growthexperiments-structuredtask-onboarding-dialog-title |
| growthexperiments-addlink-onboarding-dialog-label-skip-all | growthexperiments-structuredtask-onboarding-dialog-label-skip-all |
| growthexperiments-addlink-onboarding-dialog-dismiss-checkbox | growthexperiments-structuredtask-onboarding-dialog-dismiss-checkbox |
| growthexperiments-addlink-onboarding-dialog-label-previous | growthexperiments-structuredtask-onboarding-dialog-label-previous |
| growthexperiments-addlink-onboarding-dialog-label-next | growthexperiments-structuredtask-onboarding-dialog-label-next |
| growthexperiments-addlink-onboarding-dialog-get-started-button | growthexperiments-structuredtask-onboarding-dialog-get-started-button |