[BRE-2166] Add metadata to container images

[vgrassia]

🎟️ Tracking

BRE-2166

📔 Objective

This PR adds metadata to our container images making it easier to debug issues.

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

This PR adds OCI image metadata to the Docker build matrix in .github/workflows/build.yml, introducing a per-project description matrix key, a custom-meta step that emits label/annotation pairs to GITHUB_OUTPUT, and a docker/metadata-action step whose outputs feed labels/annotations into the existing docker/build-push-action step. All 16 matrix entries received a description, so the 'Bitwarden service' fallback is defensive only. Values are passed via env: rather than inline ${{ }} interpolation inside the shell body, which avoids script injection, and the new action is SHA-pinned with a version comment consistent with the rest of the workflow.

Code Review Details

No findings met the threshold for posting.

Notes considered and dismissed during review:

• org.opencontainers.image.revision correctly uses github.event.pull_request.head.sha for PR builds, matching the ref used by the actions/checkout step, rather than the merge commit SHA.
• com.bitwarden.project set via the workflow overlaps with util/Setup/Dockerfile's existing com.bitwarden.project="setup" label, but the values agree (matrix name is lowercased), so no conflict.
• Descriptions contain no commas, so list parsing of the multi-line labels/annotations inputs is unambiguous.
• DOCKER_METADATA_ANNOTATIONS_LEVELS: index,manifest is the appropriate level set for the multi-platform (linux/amd64,linux/arm/v7,linux/arm64) pushes performed here.