Private /ask and /edit, ability to set model in conversations

What's Changed

• Ability to do /gpt ask privately, only visible to you
• Add the ability to set model in threads by @Hikari-Haru in https://github.com/Kav-K/GPT3Discord/pull/127

Full Changelog: Kav-K/GPT3Discord@v9.0.4...v9.1