Add shared VoteStreaks progress groups

[semisolar]

Adds optional progress groups for new VoteStreaks.

This lets multiple milestones share the same streak progress state, while each milestone still has its own amount, recurring setting, and rewards.

Progress groups can also be reset by their group id with ResetVoteStreaks. This builds on the reset command added in #1519.

In the example below, DailyStreak3 and DailyStreak7 are both part of the MyProgressGroupOne progress group. This lets those milestones share the same missed period settings, and more importantly, the same stored progress value. That means the whole progress group can be reset or restored at once, instead of needing to reset or edit every milestone separately.

Example grouped setup:

VoteStreaks:
  ProgressGroups:
    MyProgressGroupOne:
      Type: DAILY
      VotesRequired: 1
      AllowMissedAmount: 1
      AllowMissedPeriod: 7
      Milestones:
        DailyStreak3:
          Enabled: true
          Amount: 3
          Recurring: false
          Rewards:
            Messages:
              Player: "&aYou reached a 3 day streak"

        DailyStreak7:
          Enabled: true
          Amount: 7
          Recurring: false
          Rewards:
            Messages:
              Player: "&aYou reached a 7 day streak"

Existing ungrouped setup still works the same:

VoteStreaks:
  DailyStreak14:
    Type: DAILY
    Enabled: true
    Requirements:
      Amount: 14
      VotesRequired: 1
    AllowMissedAmount: 1
    AllowMissedPeriod: 7
    Recurring: false
    Rewards:
      Messages:
        Player: "&aYou reached a 14 day streak"

Existing flat VoteStreak configs should keep working the same unless ProgressGroups is used.

If accepted, this will need a wiki update with the new ProgressGroups config format.