Add code for Longest increasing subsequence in DP

[amankhanathani]

Is your feature request related to a problem? Please describe.
Given an array find the Longest increasing subsequence.
In interviews they might ask these as what is the max length of sub array.
Describe the solution you'd like
Suppose A={1,4,2,4,3} we can have increasing subsequence 1,2,3 or 1,2,4.
Brute force takes exponential time, so this is preferred.
Do you want to work on it
Ill add comments and code using C++.

[prakharshreyash]

@amankhanathani Can I work on this issue using c++?

[agrlmuskan]

@amankhanathani please assign this issue to me in C++.I am a GSSOC'21 participant

[tanyajha16]

hey!! @amankhanathani can i use this as my first open source contribution?