title: Register joined/abandoned in og group
body: <p>I need register in a custom log when a user requests to join a group. Then I need register that the user has joined in the group or has abandoned this.</p>
  
  <p>I do not know how to do it without changing the orginal module. I do not know how I can extend the functionality of a contributed module correctly.</p>
  
  <p>Appreciate any guidance to investigate. Thanks :)</p>