Implemented
Editable Out of Office Default Message
When making an Annual Leave and setting the Out Off Office option, the message "I am currently out of the office and not responding to emails. I will return on DD/MM/YYYY" has to be manually edited each time a new request is made.
It would be a good idea to customize this message for the whole company.
This feature has now been implemented. You can set up your company default out of office message by going to System Config > General Settings > Leave > Gmail Out of Office.