Make Username Format configurable

[Wissididom]

What the PR does:

• Fixes
  • /mod score failing because the subcommandgroup is null, which was to be checked against the stringscore to see if the command was executed. This was fixed by just moving the score case into a new switch inside the default case.
• Added
  • /settings username set <mode> to set the username format. The mode is an integer option with different names, so the bot receives the integer option from Discord on interactionCreate so that there doesn't have to be string comparisons.
  • /settings username show to just simply show what the setting is currently set to
  • /settings username help just like the other commands to explain the newly added commands
  • /settings username unset to just set the username mode to 4 (it's a zero-based integer in the order of the list that is in the linked issue, 4 is the default we decided on there).
  • Since the Championship is not implemented yet, the only place that had to handle it was leaderboard.ts (Checked with git --no-pager grep username).

[Wissididom]

LGTM and works as expected from what I can tell. Feel free to merge if it looks good to you too.

[GeorgeCiesinski]

Looks good to me too. Thanks for the update!