Add a metric to track users joining / leaving the beta group

Co-authored-by: Saray Cabrera Padrón <scabrerapadron@suse.de>

src/api/app/models/user.rb

@@ -100,6 +100,7 @@ class User < ApplicationRecord
   validates :password, confirmation: true, allow_blank: true
 
   after_create :create_home_project, :track_create
+  before_save :send_metric_for_beta_change, if: :in_beta_changed?
 
   def track_create
     RabbitmqBus.send_to_bus('metrics', "user.create id=#{id}")
@@ -840,6 +841,11 @@ def mark_login!
     update_attributes(last_logged_in_at: Time.now, login_failure_count: 0)
   end
 
+  def send_metric_for_beta_change
+    channel = (in_beta? ? 'joined_beta' : 'left_beta')
+    RabbitmqBus.send_to_bus('metrics', "user.#{channel} value=1")
+  end
+
   private
 
   def password_validation