Python HL SDK: enable object stat API request user metadata and presign

[nopcoder]

The Python HL SDK stats API call object_stat without a way to request the user_metadata and presign.

Suggesion:

Provide a way to pass optional presign and user_metadata optional bool to the request, same as the generated API provided from the generated SDK.

import lakefs

main_branch = lakefs.repository("quickstart").branch("main")
stat = main_branch.object(path="README.md").stat(presign=True, user_metadata=True)