add /welcome system

[chevyboys]

• [ ] create message create event handler for welcoming new and returning users.
  • [ ] Ensure database entries are updated if new
  • [ ] Ensure welcome message for returning users is a welcome back message.
  • [ ] Ensure users that have been targeted by /smite do not receive welcome messages, but that the database is updated.
• [ ] generate welcome message using our updated welcome message calculations from the google sheet dynamically
• [ ] create buttons and responses from the Google sheet
• [ ] create /welcome sub commands for temporarily editing the welcome message
  • [ ] /welcome reset - sets to default behavior.
  • [ ] all subcommands except reset will have the following options: [title] [image url] [description] [days?]
  • [ ] all sub commands must enforce character limits.
  • [ ] all sub commands will send embeds
  • [ ] /welcome append
  • [ ] /welcome override