Added code for quick sort in cpp

[shraddha2803]

#329 The provided C++ code implements the quicksort algorithm to efficiently sort an array of integers. The 'partition' function selects a pivot element and rearranges the array so that all elements less than the pivot are on its left, and all elements greater are on its right. The 'quicksort' function is a recursive algorithm that sorts the sub-arrays before and after the partition point.