Set bounds for parameter estimation.
A dictionary with parameter names as keys and the respective bounds intervals as values (lists/tuples/arrays). The available parameter names are in
self.param_names. The default option is
None, in which case the traditional (nonlinear) bounds as described in  are used.
Hyndman, R.J., & Athanasopoulos, G. (2019) Forecasting: principles and practice, 3rd edition, OTexts: Melbourne, Australia. OTexts.com/fpp3. Accessed on April 19th 2020.