as_task_*_st and friends could allow setting column roles directly

[pat-s]

We could support this via the ellipsis. Otherwise setting the respective column roles could be somewhat easily forgotten.
On the other hand behaviour would differ than compared to as_task_*() from mlr3 as such custom conversions would not be supported there.

@be-marc what do you think?

Example:

data("cookfarm_sample", package = "mlr3spatiotempcv")

# data.frame
as_task_regr_st(cookfarm_sample, target = "PHIHOX",
  coords_as_features = FALSE,
  crs = 26911,
  coordinate_names = c("x", "y"),
  column_role_space = "foo",
  column_role_time = "time"
)

```

[pat-s]

Thinking about it once more, I guess leaving it as it is might be best.
This change would also be very niche and the behavior does not appear in other mlr3 packages, so it would probably not be used much.

[pat-s]

With *ST tasks becoming the main Task type (again), we probably want to have this. Maybe not with space and time col roles but groups instead - but the general feature to specify the grouping during task construction.