warn about deploy attributes ignored in standalone mode

[veerareddyvishal144]

Fixes #13150

Compose silently ignores several deploy sub-attributes outside Swarm mode (e.g. a service with deploy.update_config behaves as if it wasn't set). Per the Compose spec the runtime should warn about unsupported attributes.

Change

• New cmd/compose/warnings.go: after the project model loads (ProjectOptions.ToProject), emit one warning per service listing the ignored deploy attributes it sets: placement.constraints, placement.preferences, update_config, rollback_config, endpoint_mode, mode. Attributes that are still honored (replicas, device reservations, restart_policy fallback) are deliberately excluded.
• Unit tests for the collector (nil/empty/supported-only/ignored).

Verification

• go test ./cmd/compose/ passes (incl. new tests); golangci-lint 0 issues; gofmt clean.
• End-to-end with a locally built binary: a service with update_config + placement.constraints prints Service "web" uses deploy attributes that are ignored by Compose in standalone mode: placement.constraints, update_config on stderr; a replicas-only service stays silent.