Adds the way to specify the topic on channel creating.
Created by: Kiritsu
Summary
Currently, we can't create a channel and specify its topic directly, we have to call ModifyAsync. As seen here: https://discordapp.com/developers/docs/resources/guild#create-guild-channel we can specify the topic in the request payload.
Details
Simply added the topic in different channel creation method Added the topic property in the request payload