Add a composite_operation field

[finnagin]

• [x] Modify schema.json to allow the validator to pass with the additional field
• [x] Identify all of the composite operations
• [x] Add an additional field named composite_operation to each of those containing an ordered list of the operations used.

[finnagin]

@patrickkwang @cbizon @dkoslicki @edeutsch Does anyone know if there is another composite operation besides lookup and lookup+score? I just looked through the yamls and none of the other operations looked like composite operations to me.

[dkoslicki]

Not that I'm aware of

[dkoslicki]

PR merged