feat: Add Bangla language support for Bangladeshi holidays

[jfBiswajit]

Contributing a new country ?

• Have you checked to ensure there aren't other open Pull Requests for the same country?

1. Create a new class in the Countries directory. It should extend the Country class.
2. Add a test for the new country in the tests directory.
3. Run the tests so a snapshot gets created.
4. Verify the result in the newly created snapshot is correct.

[Nielsvanpach]

Thanks. Does it make sense to return Bangla by default instead of English?

[jfBiswajit]

Thanks! Please check the changes. It returns Bangla names in English instead of Bangla font.

[Nielsvanpach]

Thanks!