Can i implement the drag and drop stickers in the conversation on my own I Message Sticker app ?

Yes, you can. Use a CollectionView for the MSStickers.

You don't have to do that, you could present your MSStickerView in a number of ways. But if you want to create something similar to the functionality of the default packs, then most people go with a CollectionView (I think I remember reading Apple recommended that).