[FEAT] ESRNN Model

[AzulGarza]

A user requested to include the ESRNN model (available in previous versions of NeuralForecast). The user tried to use this version but it does not allow more than one exogenous variable.

[Yasslight90]

Hi @federicogarza. Do you plan to add the ensembling attribute as in the original implementation of @kdgutier

model= ESRNN(ensemble=True)

Thanks :-)

[marcopeix]

Closing because no work has been done on this for the past 3 years, not sure if ESRNN is still a relevant addition today.