I run stac-catalog with using pgstac, but it is not clear for me how to use it. My expectation that i can take [pystac_client](https://pystac-client.readthedocs.io/en/stable/) and create Collection with some Items, but I don't see such methods for that. I've found [this](https://github.com/stac-utils/pystac/blob/main/docs/tutorials/how-to-create-stac-catalogs.ipynb) notebook, but it shows how to create static-catalog in file Could you provide example how to create items.