bot: Create a settings command

[rsodre]

Tasks

• Create a settings command
• Available only to admins (check some permissions, not role name)
• Boolean settings for:
  • new/updated Duelist notifications (bot: New Duelists Notification #14)
  • Duels notifications (bot: Challenge Notifications #4)
  • Duelist turn notifications (bot: Discord Users notifications #6)

[Pycomet]

Hey @rsodre, this looks like a great first issue for me. Can I take this on?