Add methods for retrieving batches for a project

[shantanubala]

Description

I talked to a user today who was trying to upload images via API, but was wondering if there was a way to retrieve upload batches via the Python SDK. It turns out there's no Python SDK function for fetching the batches, so I've implemented them in this PR with unit tests.

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

How has this change been tested, please provide a testcase or example of how you tested the change?

Added unit tests and tested the SDK locally.

Any specific deployment considerations

No

Docs

I'll update these docs if the PR looks good: https://docs.roboflow.com/api-reference/batches