Call populate_match_below when a match is finished

app/controllers/matches_controller.rb

@@ -14,9 +14,7 @@ class MatchesController < ApplicationController
   def update
     new_state = match_params['state']
     if new_state == 'finished'
-      # implement logic to move the winning team into the next stage
-      match_params['state'] = 'finished' # or 'team2_won' or 'undecided'
-      render json: {}, status: :not_implemented
+      PlayoffStageService.populate_match_below(@match) unless @match.group_match?
     end
     if @match.update(match_params)
       render json: @match