Added new flask course (bn)

[kausar2nd]

What does this PR do?

Added new flask course in Bangla

For resources

Description

Why is this valuable (or not)?

It goes over the whole flask within 2 hours

How do we know it's really free?

It's available on Youtube

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

Yes, it is a course

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).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!

[eshellman]

Thanks, and welcome to free-programming-books!