Applies a John Draper transformation (1) to spelected etas
Initial estimate for lambda is 0.1 with bounds (-3, 3).
(1) John, J., Draper, N. (1980). An Alternative Family of Transformations.
Journal of the Royal Statistical Society. Series C (Applied Statistics),
29(2), 190-197. doi:10.2307/2986305
if (FALSE) {
model <- load_example_model("pheno")
model <- transform_etas_john_draper(model, c("ETA_CL"))
model$statements$before_odes$full_expression("CL")
}