Expose hooks when important events occur

[inderpreet99]

Expose hooks for when important events happen, so developers can programmatically hook-in to send notifications. Example events:

• Cloning a post
• Draft saved on the clone
• Publishing the clone

Ideally, the plugin could help facilitate these notifications.

Requested in https://wordpress.org/support/topic/can-we-edit-user-role-access-so-editors-are-unable-to-replace-original/