Add SBOM attestations to Docker images (#18252)

Adds SBOM attestations
https://docs.docker.com/build/metadata/attestations/sbom/

Requires https://github.com/rust-secure-code/cargo-auditable/pull/236
for our uv binaries and their dependencies to be included in the SBOM

You can inspect the SBOM with, e.g.:

```
docker buildx imagetools inspect ghcr.io/astral-sh/uv-dev:sha-ece6427 --format '{{json .SBOM}}' | jq
docker buildx imagetools inspect ghcr.io/astral-sh/uv-dev:sha-ece6427-python3.9-trixie --format '{{json .SBOM}}' | jq
```

Also explicitly sets
https://docs.docker.com/build/metadata/attestations/slsa-provenance/#max
but there appears to be no change as all of the max SLSA data is already
present.

.github/workflows/build-docker.yml

@@ -161,6 +161,8 @@ jobs:
           push: ${{ needs.docker-plan.outputs.push }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          provenance: mode=max
+          sbom: true
           # TODO(zanieb): Annotations are not supported by Depot yet and are ignored
           annotations: ${{ steps.meta.outputs.annotations }}
 
@@ -315,6 +317,8 @@ jobs:
           push: ${{ needs.docker-plan.outputs.push }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          provenance: mode=max
+          sbom: true
           # TODO(zanieb): Annotations are not supported by Depot yet and are ignored
           annotations: ${{ steps.meta.outputs.annotations }}