Creates a ParallelMaybelist using a Builder computation expression.

Returns: Builder

Example

 let emptyStep1 = Step.create "empty1" { () }
 let emptyStep2 = Step.create "empty2" { () }
 let emptyStep3 = Step.create "empty3" { () }

 let condition = true

 let pipeline =
     Pipeline.create "example" {
         run_parallel_maybes {
             run emptyStep1
             run_maybe emptyStep2 condition
             run emptyStep3
         }
     }