Add scenario to the model

Usage

add_scenario(
  model,
  name = "expansion",
  origin = "baseline",
  origin_start = NA,
  origin_end = NA,
  shock
)

model: SFC model object
name: string name of scenario, defaults to 'expansion'
origin: string name of origin scenario, from which the new scenario will be created, defaults to 'baseline'
origin_start: numeric period number from origin scenario from which the new scenario will begin
origin_end: numeric period number from origin scenario on which the new scenario will end
shock: shock object from create_shock() and add_shock()

updated SFC model object containing added scenario