blob/s3blob: add support for conditional writes

[SoMuchForSubtlety]

Is your feature request related to a problem? Please describe.

S3 recently added support for conditional writes¹ by setting the If-None-Match or If-Match headers. This is great for managing concurrent operations.

Describe the solution you'd like

Exposing this option through the standard API would be great

Describe alternatives you've considered

GCS also supports request preconditions². If-None-Match and ifSourceGenerationMatch could be mapped to a common API, but this will only cover a subset of the possible use cases.

Footnotes

1. https://aws.amazon.com/about-aws/whats-new/2024/11/amazon-s3-functionality-conditional-writes/ ↩

2. https://cloud.google.com/storage/docs/request-preconditions ↩

[vangent]

Does Azure support it?

[SoMuchForSubtlety]

Azure and Minio both support If-None-Match and If-Match.