Add Email notification system

[akshatnema]

Reason/Context

• Why we need this improvement?
  Presently, we don't have any notification system in our application and the opportunities, that are available for short durations only, need to be notified to end users at correct time.
• How will this change help?
  This change will help them to remain up to date with the current opportunities coming in the tech field.

Description

• What changes have to be introduced?
  Email Notifications + SMS notifications (if possible)
• Will this be a breaking change?
  No
• How could it be implemented/designed?
  A cron job is needed to catch the recent opportunities from the database and make a notification system to send notifications to subscribed users.