Docs: Python integration doc needs update

[N-o-Z]

https://docs.lakefs.io/integrations/python.html

Due to code changes, we need to go over the guide and update the code snippets. One example:

branch1 = lakefs.repository("example-repo").branch("experiment1").create(source_reference_id="main")

For branch creation parameter name was changed from source_reference_id to source_reference.