Add mongoDB course/book to check_urls=free-courses-en.md free-programming-books.md

[kadhirash]

What does this PR do?

Add resources | Improve repo

For resources

Description

• Fixes Added more course links for databases #3890
  • Organize free-courses-en.md
    • NoSQL and SQL sections under Database, as agreed upon in Added more course links for databases #3890
  • Add MongoDB course under NoSQL
  • Add MongoDB book under NoSQL, tutorial points is more so a book. Refer to discussion on Should tutorialspoint resources be in books, or in courses? #4573

Why is this valuable (or not)?

-Adds course and book; Cleans PR; improves repo

How do we know it's really free?

• Free course and book site online!

For book lists, is it a book? For course lists, is it a course?

• Yes

Checklist:

• Read our contributing guidelines
• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction)

Followup

• Check the output of Travis-CI for linter errors!