Forward person when a programming group is created with them

Further, we remove the "check invitation" button and extract some methods to our new ProgrammingGroups object in JavaScript.

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

app/channels/pg_matching_channel.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class PgMatchingChannel < ApplicationCable::Channel
+  def subscribed
+    set_and_authorize_exercise
+    stream_from specific_channel
+  end
+
+  def unsubscribed
+    # Any cleanup needed when channel is unsubscribed
+    stop_all_streams
+  end
+
+  def specific_channel
+    "pg_matching_channel_exercise_#{@exercise.id}"
+  end
+
+  private
+
+  def set_and_authorize_exercise
+    @exercise = Exercise.find(params[:exercise_id])
+    reject unless ExercisePolicy.new(current_user, @exercise).implement?
+  end
+end