S3 IAM Authentication fails due to library bug

Environment

• Mattermost Server: 5.22.0

Steps to Reproduce

1. Upgrade to version 5.22.0 from 5.21.0 with Amazon S3 file storage with IAM credentials

Expected Behavior

S3 file uploads work as expected

Observed Behavior

All S3 related actions fail and this message is printed repeatedly to the logs:

Proposed Fixes

There is an error in the minio-go library reported in this issue which was resolved with this pull request to the library. We need to upgrade to version 6.0.45 of the library or later.