Creates a reaction and adds it to a message. For an example, see Add a reaction to a message. Requires user authentication with one of the following authorization scopes: - https://www.googleapis.com/auth/chat.messages.reactions.create - https://www.googleapis.com/auth/chat.messages.reactions - https://www.googleapis.com/auth/chat.messages - https://www.googleapis.com/auth/chat.import (import mode spaces only)