Fix S3 compatibility in Workhorse uploads for non-AWS S3 providers

What does this MR do and why?

GitLab 18.2 updated the aws-sdk-go-v2/service/s3 from v1.66.0 to v1.80.2 in !189094 (merged).

As discussed in https://github.com/aws/aws-sdk-go-v2/issues/3003 and https://github.com/aws/aws-sdk-go-v2/discussions/2960, github.com/aws/aws-sdk-go-v2/service/s3 v1.73.0 changed the AWS SDK default object integrity behavior. Third-party S3 providers, such as Linode, may fail with XAmzContentSHA256Mismatch error as a result.

To restore compatibility, configure the client only to do request checksum calculations when required.

References

ZD: https://gitlab.zendesk.com/agent/tickets/642635

How to set up and validate locally

1. Sign up for a Linode S3 account: https://www.linode.com/products/object-storage/
2. In your gdk.yml, add the Linode configuration. For example for a bucket called stanhu-test, I did:

object_store:
  consolidated_form: true
  enabled: true
  connection:
    provider: AWS
    aws_access_key_id: REDACTED
    aws_secret_access_key: REDACTED
    region: us-sea-1
    endpoint: https://us-sea-1.linodeobjects.com
    path_style: false
  objects:
    artifacts:
      bucket: stanhu-test/artifacts
    backups:
      bucket: stanhu-test/backups
    external_diffs:
      bucket: stanhu-test/external_diffs
    lfs:
      bucket: stanhu-test/lfs-objects
    uploads:
      bucket: stanhu-test/uploads
    packages:
      bucket: stanhu-test/packages
    dependency_proxy:
      bucket: stanhu-test/dependency-proxy
    terraform_state:
      bucket: stanhu-test/terraform
    pages:
      bucket: stanhu-test/pages
    ci_secure_files:
      bucket: stanhu-test/ci-secure-files
    gitaly_backups:
      bucket: stanhu-test/gitaly-backups

3. Run gdk reconfigure.
4. Upload a file in an issue.

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