Add "Rat in a maze" problem in Backtracking

[Aayushadh]

Rat in a maze is one of the most popular backtracking problem, I would like to add it.

[Aayushadh]

I had added this problem to backtracking folder, check it here - #309

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Please reopen this issue once you commit the changes requested or make improvements on the code. Thank you for your contributions.