Python: Fix positional argument issue for load_catalog API

[cabhishek]

• load_catalog API does not require the name of the catalog to be passed in as it can figure that out from ENV var or Config files.

Test code

from pyiceberg.catalog import load_catalog

catalog = load_catalog() # <- should load the default-catalog

catalog.list_namespaces()

Before PR

TypeError: load_catalog() missing 1 required positional argument: 'name'

After PR

Above code should load the default catalog and not throw any error.

[HonahX]

LGTM! Thanks for the fix @cabhishek

[Fokko]

This makes sense, thanks @cabhishek

[Fokko]

Merging this for the upcoming 0.5.0 release 🚀