Counting Sort[CPP]

[Phagun26]

This issue is about [Algo/DS Name](link to resource for the Algo/DS).

• [ X] Issue Title is in form Algo/DS Name [Language].
• [ X] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• [ X] This Algo/DS is worth adding to this repository.
• [ X] Assign this issue to me (I want to work on this).
  • [X ] I ensure that I am not already assigned to 2 or more issues.
• [ X] I will send my PR only after I'm assigned to this issue by any maintainer.
• [X ] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.