* configure Loki for local development
Extend our docker compose setup to include Loki (along with promtail), scraping `logs/*.log` to ingest development logs as well as all logs from running containers.
While we're in here, teach Prometheus to scrape metrics from Docker containers too.
* tweak promtail labels
* document extra services in config.mk
* update home.json
Don't list Prometheus and Grafana as targets in the `start_dependencies` target of the docker compose file used in CI and local development. These can still be started by hand, but will no longer waste resources in CI, nor fail build spuriously if they fail to come online.
