[FEATURE] maximum flow algorithm

[offamitkumar]

in the graph section, maximum flow algorithm implementation with Ford Fulkerson & Edmond Karp method are not present.

[ayaankhan98]

go ahead and implement, we will be looking for your PR and don't forget to mention this issue #790 in PR

[offamitkumar]

@ayaankhan98 my pull request is still not merged, would you please merge it.