`arx_fcast_epi_workflow` is not particularly user friendly

There are apparently existing OKrs about this, but I wanted to put in an issue as well. I was attempting to modify just one step in an existing workflow (to allow for more `NA` filling in the frosting layer). Hypothetically there is a way to do this by intervening between `arx_fcast_epi_workflow` and `fit`, but the models are buried far too deep (`ewf$pre$actions$recipe$recipe$steps`) to be usable by someone only somewhat familiar with the package.

An idea would be to include a function like `get_step(workflow,n)` which could be used to get or set the nth step in the workflow.