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/config.mk

@@ -5,7 +5,7 @@
 # Enable services to be run in docker.
 #
 # Possible options: mysql, postgres, minio, inbucket, openldap, dejavu,
-# keycloak, elasticsearch, prometheus, and grafana.
+# keycloak, elasticsearch, prometheus, grafana, loki and promtail.
 #
 # Must be space separated names.
 #