KMP String matching algorithm in C++

[Rohit-varma]

I would like to contribute a C++ solution for KMP String matching algorithm. @Anishukla could you assign this issue to me?

[Rohit-varma]

@durgesh-4526 I think you misunderstood, I opened this issue so that it would get assigned to me by the maintainer and then I wanted to make a PR.