Manage sf_hydro_regions object

Should we keep them as datasets or make a function that returns a different object depending on a 'territory' argument?

Currently, the package contains the following data sets:

• sf_hydro_regions_gua
• sf_hydro_regions_met
• sf_hydro_regions_mtq
• sf_hydro_regions_myt
• sf_hydro_regions_reu

They could therefore be replaced by the following function:

get_sf_hydro_regions(territory = "Mayotte")