Fix warning messages for milestone promotion and label promotion
These are the current warning messages. They are incorrect:
Warning messages to implement in this issue
Promoting [milestone] will make it available for all projects inside [Group name]. Existing project milestones with the same name will be merged. This action cannot be reversed.
Promoting [label] will make it available for all projects inside [Group name]. Existing project labels with the same name will be merged. This action cannot be reversed.
Edited by Victor Wu