Docker: use command instead of entrypoint

Describe the bug Cannot run custom commands in the image.

See also

• https://github.com/grafana/grafana/discussions/38361
• https://github.com/grafana/grafana/issues/83865
• https://github.com/docker-library/official-images/blob/d28cb89e79417cac50c2a8ae163a9b3b79167f79/README.md#consistency

To Reproduce Steps to reproduce the behavior: docker run --rm grafana/loki echo "test" Returns failed parsing config: config.yaml,config/config.yaml does not exist, set config.file for custom config path

Expected behavior Should run echo "test" inside the container.

Patch would be very similar to the one described in https://github.com/grafana/grafana/discussions/38361.

Environment:

• Docker

Screenshots, Promtail config, or terminal output n/a