Add `"xarray:open_dataset_kwargs"` to Sentinel-3 SLSTR Level-2 LST asset LST

[konstntokas]

In Sentinel-3 SLSTR Level-2 LST item, there is the asset "lst". This is a dataset and the {"xarray:open_dataset_kwargs": {'chunks': {}, 'engine': 'eopf-zarr', 'op_mode': 'native'}} may be added, as it is done for datasets (subgroups) in Senitnel-2 and Sentinel-1. I have tested the access via xarray-eopf which works fine.