Add waiting room to create programming groups (#1919)

Co-authored-by: Sebastian Serth <Sebastian.Serth@hpi.de>

app/models/pair_programming_waiting_user.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class PairProgrammingWaitingUser < ApplicationRecord
+  include Creation
+
+  belongs_to :exercise
+  belongs_to :programming_group, optional: true
+
+  enum status: {
+    waiting: 0,
+    joined_pg: 1,
+    disconnected: 2,
+    worked_alone: 3,
+    created_pg: 4,
+  }, _prefix: true
+
+  validates :user_id, uniqueness: {scope: %i[exercise_id user_type]}
+  validates :programming_group_id, presence: true, if: -> { status_joined_pg? || status_created_pg? }
+
+  after_save :capture_event
+
+  def capture_event
+    Event.create(category: 'pp_matching', user:, exercise:, data: status.to_s)
+  end
+end