ci: publish multi-arch Docker images from tags

[lwmacct]

Summary

• trigger Docker publishing only when a v* Git tag is pushed
• build linux/amd64 and linux/arm64 images on native GitHub runners and merge their digests into one manifest
• publish the exact Git tag, such as v1.2.3, together with latest
• update the Docker deployment documentation for the tag-driven release flow

Validation

• actionlint -color .github/workflows/docker-release.yml
• git diff --check
• DOCKER_CONFIG=/tmp/asterrouter-empty-docker-config ASTER_TEST_ARTIFACT_DIR=/tmp/asterrouter-docker-workflow-check ASTER_CONTAINER_TEST_VERSION=0.24.0 bash scripts/test-container.sh on native linux/arm64