Prevent users from volunteering to an past events

[ahnwarez]

This is description should be refined

Users should not be able to Volunteer to past events.

In the Backened:

• The POST / route in server/routes/volunteers.js should check for the event date, if it's greater than today then add the volunteer, else repond with a status code 500 and a message to reject the request with a message " Sorry, but you cannot volunteer to an expired event ".

In the Front-end:

• Past events are already rendered but they get displayed at the bottom, disable the volunteer button and use a different background color, maybe use a dull color such as grey to visually indicate that the event is inactive.