python(feature): file attachments upload + download service

[solidiquis]

Changes

Added sift_py.file_attachment module to leverage the file attachments API. The FileAttachmentService from said module allows for ergonomic uploading, downloading, retrieving attachments for various entities, as well as bulk deleting.

Unit testing + documentation updates included. Examples will be added in a separate PR, though the documentation already includes plenty of examples.

[zachAtSiftStack]

nit: docs typo, drop the word "support"

it also support provides utilities....

[zachAtSiftStack]

The error log for a bad api key or run id (not sure which) wasn't really helpful

(filevenv) (venv) ➜  ingestion_with_python_config git:(python/feature-file-attachment) ✗ python3 test_file_attach.py
Traceback (most recent call last):
  File "/Users/zachplunkett/Code/sift/python/examples/ingestion_with_python_config/test_file_attach.py", line 45, in <module>
    remote_file = file_attachment_service.upload_attachment(
  File "/Users/zachplunkett/venvs/filevenv/lib/python3.9/site-packages/sift_py/file_attachment/service.py", line 80, in upload_attachment
    remote_file_id = self._upload_service.upload_attachment(
  File "/Users/zachplunkett/venvs/filevenv/lib/python3.9/site-packages/sift_py/file_attachment/_internal/upload.py", line 90, in upload_attachment
    raise Exception(response.text)
Exception

But after that it worked as expected :)

[zachAtSiftStack]

LGTM, Approving