Add new end-points for improved temporal statistics capabilities of GRASS GIS 8.3

[ninsbl]

Would be nice to be able to retrieve univariate statistics from STRDS synchronously, comparable to how e.g. "raster_layers" are retrieved. Improvments for t.rast.univar give some new possibilities.

Here I think of something like e.g. this:

http://actinia.io/api/v3/locations/nc_spm_08/mapsets/user2/strds/modis_lst/univar_statistics?where=start_time>='2023-04-24 00:00:00' and start_time<='2023-04-25 00:00:00'&zones=counties@PERMANENT&nprocs=4

The same approach may be used for r.stats with STRDS as implemented in t.rast.stats