enhance/validation to check cyclic paths in GraphUtil -> getAllPaths

[JasonShin]

Context:

As a result of implementing the initial version of GraphUtil -> getAllPaths, we can now retrieve all the possible paths from a vertex in a JSON graph. In addition to getting the paths, it should also run a validation in prior to creating a pipeline to check any cyclic paths. Example of a cyclic-graph is

In the diagram, cycle happens for 0 -> 2 -> 1 and 0 -> 3 -> 4.

I think we should not allow any cyclic tasks due to the potential performance issue caused by the infinite loop.

TODO:

• Implement a cyclic graph validation method; implement in the GraphUtil class https://github.com/StormwindHQ/GraphPilot/blob/master/app/utils/GraphUtil.scala#L15
• Test the validation

References:

• Basics of Graph Theory: https://medium.com/basecs/a-gentle-introduction-to-graph-theory-77969829ead8