Get metadata consistency policy from contract

[smallhive]

Closes #1148.

[Copilot]

Pull Request Overview

This PR updates the handling of container placement policies by introducing a composite PlacementPolicy type that separates the placement and metadata consistency aspects. Key changes include:

• Updating usage of container placement policies to reference the Placement field rather than the full policy.
• Changing the configuration and unmarshaling logic to incorporate a new Consistency field.
• Adjusting related API interfaces and test mocks to use the new PlacementPolicy type.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/neofs/neofs.go	Updates in CreateContainer to use the Placement and Consistency fields from Policy.
cmd/s3-gw/storage_policy_provider.go	Refactors GetPlacementPolicy to unmarshal into the new PlacementPolicy type.
cmd/s3-gw/storage_policy.go	Updates function signatures to use the new PlacementPolicy type.
cmd/s3-gw/app.go	Introduces configuration handling for ContainerMetadataPolicy.
api/layer/neofs_mock.go	Updates test mocks to accommodate the new PlacementPolicy structure.
api/layer/neofs.go	Changes the PrmContainerCreate type to use the new PlacementPolicy type.
api/layer/layer.go	Introduces the PlacementPolicy type and related constants.
api/handler/put.go	Constructs PlacementPolicy values with explicit Version, Placement, and Consistency.
api/handler/api.go	Updates interface definitions to return the new PlacementPolicy type.