Backup Fails To Write File To Backblaze

Problem/Motivation

When running a backup of the database to Backblaze, I receive the following error:

"The backup file could not be saved to 'backblaze://' because Backup and Migrate does not have write access to that directory or there is something wrong with the Flysystem configuration"

I originally reported this on backup_migrate_flysystem, but the problem here is that BackBlaze is not fully compatible with the AWS S3 PHP API. See the "Unsupported Features" section of https://www.backblaze.com/docs/cloud-storage-s3-compatible-api

Steps to reproduce

Proposed resolution

The following patch for flysystem_s3 exposes the 'request_checksum_calculation' config so the value 'when_required' can be set in the website settings.php file.

Remaining tasks

User interface changes

API changes

Data model changes