Add triplets endpoint

[agent515]

Please describe the feature you want this project to offer
The endpoint /triplets which will tell, if the given sides form a right-angled triangle.

Describe the solution you'd like

1. Check all sides are non-zero positive integer
2. Check if sides form a valid triangle
3. Check if sides form a right-angled triangle using Pythagoras theorem

Additional context (Optional)
Also, add tests for the same.

1. form a right-angled triangle (200)
2. do not form a right-angled triangle (200)
3. do not form a triangle (200)
4. bad credentials (400)