Alternative workflow processor behavior when order is used

[advancedlogic]

Currently the workflow processor runs branches trying to infere the DAG automatically or using order. The behavior of order prioritizes parallelism over sequential so in [ [ A, B], [C] ], A and B are processed simultaneously and then C is executed. When the graph becomes complex, it's hard to keep track of every parallel processing and it would be easier to describe the order as a graph with nodes and edges.
Considering the example in the documentation:

      /--> B -------------|--> D
     /                   /
A --|          /--> E --|
     \--> C --|          \
               \----------|--> F

described as:
[ [ A ], [ B, C ], [ E ], [ D, F ] ]

could become a list of edges:

[ [ A, B], [A, C], [B, D], [C, E ], [ C, F ], [ E, F ] ]

[jem-davies]

#2599 - possible overlap with this issue

As part of the PR that proposes a solution to the issue 2599 - the way the DAG is represented in Benthos Config has been altered to :

          B:
            dependency_list: ["A"]
            processors:
              ...

So each Node in the DAG has a list of it's direct dependents.