Not sure if this is a great idea but it came up as part of
TINKERPOP-2389 where there might be a need to assign both a client-side and server-side SubgraphStrategy. Currently, while not explicit, you can't assign more than one strategy of a particular type using withStrategies(). This task would make that explicit and provide a direct way for mergeable strategies to be pushed together into one. If we did that it would also simplify OptionsStrategy usage in with() step which currently finds an existing one first if present and then adds to it (otherwise creates it new).