s3_sync etag calculation is wrong because use hardcoded chunk_size

[GiuseppeChiesa-TomTom]

SUMMARY

The s3_sync module reports wrong etags compared to the one calculated from AWS S3 on server side.
The etag algorithm is based on the chunk_size used during multipart upload. The s3_sync module uses the boto3 defaults for the S3 Transfer, but the function that calculates the local etags does not use those defaults (it uses an hardcoded value instead)

ISSUE TYPE

• Bug Report

COMPONENT NAME

plugins/modules/s3_sync.py

ANSIBLE VERSION

ansible 2.10.2
  config file = None
  configured module search path = ['/Users/chiesa/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Users/chiesa/.local/pipx/venvs/ansible/lib/python3.8/site-packages/ansible
  executable location = /Users/chiesa/.local/bin/ansible
  python version = 3.8.2 (default, May  1 2020, 13:24:17) [Clang 11.0.3 (clang-1103.0.32.59)]

CONFIGURATION

no changes

OS / ENVIRONMENT

Mac OS 10.15.7

STEPS TO REPRODUCE

Upload some folder with s3_sync module and compare the local_etag calculated by the module with the S3 remote tags (calculated with the chunk_size used by boto3 - underlying library to tranfer the file)

EXPECTED RESULTS

The local_etags of the file just uploaded should match the etags on S3

ACTUAL RESULTS

The local_etags of the files just uploaded are mismatching S3 etags due to the wrong chunk_size hardcoded in the module:

DEFAULT_CHUNK_SIZE = 5 * 1024 * 1024