Creates a Seasonal-Trend decomposition using Loess model.
STLModel(s)A spec for a Julia `STLModel`, built when it is fitted (see [juliabridge::julia_spec()])
The decomposition always includes a trend component, and the loess smoothing settings, robust iterations among them, belong to the estimation settings in ForecastBaselines.jl, which `fit_baseline()` does not expose. The seasonal period is therefore the only argument.
if (FALSE) { # \dontrun{
# Monthly seasonality
model <- STLModel(s = 12)
} # }