AutoARIMA coefficients names

[Chaptyziok]

Description

Currently the exogenous features coefficients are named like ex_1, ex_2. I believe that in the original R solution they are called as names of those features. Consider to change the suffices like ex_feat1 where feat1 is a name of a feature etc. This will facilitate a correct alignment of those coefficients to the corresponding features.

Use case

No response