bot: Create my_turn command

[rsodre]

Depends on #2, #5

Tasks

• Create new command: my_turn
  • Check if the Discord User who sent the command is linked to a duelist addresses (app: Social Profile App #5)
  • If not, display a message explaining how to link (TBD), and exit
  • Display a private message to the Discord user, displaying all the Duels that are waiting for their action
  • The message content must have the same as the live_duels (bot: Duel listing commands #2) command

The ChallengeState enum:

enum ChallengeState {
    Null,
    Awaiting,
    Withdrawn,
    Refused,
    Expired,
    InProgress,
    Resolved,
    Draw,
}

Notes

• Please do not duplicate functionality!
• When displaying a message with the same contents as other messages (my_duels and duels_by_duelist, my_turn and live_duels for example), extract the message-building part to a new function that can be called by both.

[Pycomet]

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