configure Loki for local development (#26997)

* 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

server/build/docker-compose-generator/main.go

@@ -35,6 +35,8 @@ func main() {
 		"keycloak":           8080,
 		"prometheus":         9090,
 		"grafana":            3000,
+		"loki":               3100,
+		"promtail":           3180,
 		"mysql-read-replica": 3306, // FIXME: not recognizing the successfully running service on port 3307.
 	}
 	command := []string{}