Support different types of prediction

[isabelizimm]

Currently, vetiver supports the predict method when handling models. In other use cases, it maybe important to be able to use predict_proba or predict_log_proba.

[juliasilge]

On the R side, we handle this by passing in an argument about the type of predictions. It would look something like this:

pr() %>% vetiver_pr_predict(v, type = "prob")
## or 
pr() %>% vetiver_pr_predict(v, type = "quantile")
## and so on