Use native slash commands instead of exclamation marks

[aesedepece]

https://discord.com/developers/docs/interactions/slash-commands

[Tommytrg]

I've read about slash commands, and I can summarize what I read in the following points:

• Slash Commands are currently in a public developer beta. There is a discussion about this topic in discord.js repository where they advise against using it in production.
• Bot commands are not standardized. I've checked commands of commonly used bots on top.gg I've seen that each bot uses a different command structure. That could be useful to avoid collisions with other bots.
• Discord's documentation uses command examples with !

IMO, we shouldn't use slash commands in a production bot, and I would consider replacing the way we call our bot: instead of use ! we could use something unique such as: ag!