Allow user to specify recursive parameter

[maksymiuks]

Core function of your pacakge - get function calls merge_lists helper inside (https://github.com/rstudio/config/blob/main/R/get.R#L95). That helper has recursive parameter that is very important for me, as I need to read config with that parameter set to FALSE. However get function does not allow to pass this parameter to merge_lists whatsoever.

Please add ellipsis to get that will populate parameters to merge_lists are even an explicit recursive parameter that will be default TRUE.

[maksymiuks]

@jjallaire