Added sudoku solver and M-coloring

[Pranjal563]

I have added two new problem's C++ code namely Sudoku Solver and M-coloring in the repository. This will facilitate GitHub users to easily go through these problems codes.

I hope this will be a definitely a better contribution and you will merge my pull request. Thanks a lot!

[Pranjal563]

Kindly add the hacktoberfest-accepted labels in this pull request while accepting.

Also for reference I am attaching screenshots of the codes and their respective outputs below.

Problem : Sudoku Solver

Output:

Problem : M Coloring

Output :

[Pranjal563]

Please please add hacktoberfest-accepted and approved labels from label section to my pull request otherwise pull request will not be valid for hacktoberfest 2022 judgement. So please add these tags. This will take only 15 - 20 seconds. Thank You !!