varying_args.step should include a unique ID column #110
Description
Eventually, when we are filling in varying() parameters we will need to know exactly which step they belong to. The current amount of information is likely not good enough because there is no unique identifier for a recipe step (i.e. you wouldn't be able to tell apart two calls to step_pca with num_comp varying in both steps). The tibble returned by varying_args.step should include a unique id column created from:
library(recipes)
ex <- recipe(Species ~ ., data = iris) %>% step_log(Species)
ex$steps[[1]]$id
#> [1] "log_YAIYj"