Implement Application Completion Workflow with Certificate Generation and Email Notification

[mayura-andrew]

Purpose

The purpose of this PR is to fix #122

Goals

• Enable admins to change the application status to 'COMPLETE'.

• Notify mentees via email upon status change.

• Generate a completion certificate for each mentee and attach it to the notification email.

  Approach

  To achieve the above goals, the following steps were taken:

• Integrated the pdf-lib library (version 1.17.1) to modify and generate completion certificates in PDF format.

• Updated utils.ts to support sending emails with PDF attachments.

• Created a separate function dedicated to handling the PDF generation and email notification logic

• Created a new folder to store certificates

Screenshots

Checklist

• [x] This PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
• [x] I have read and understood the development best practices guidelines ( http://bit.ly/sef-best-practices )
• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

Related PRs

## Test environment - OS: Linux Mint 21.3 - Browser Firefox - Version 128.0 - Nodejs 20.15.0 ## Learning

During the development of this feature, I explored several resources to understand how to effectively use the pdf-lib library for PDF manipulation and how to attach files to emails programmatically. This included reviewing documentation, blog posts, and tutorials related to pdf-lib and email handling in Node.js applications.

[mayura-andrew]

Can you resolve the conflicts? @mayura-andrew I'm working on this