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/grafana/provisioning/datasources/loki.yml

@@ -0,0 +1,11 @@
+apiVersion: 1
+
+datasources:
+  - name:  Loki
+    type: 'loki'
+    access: 'proxy'
+    orgId: 1
+    url: 'http://loki:3100'
+    isDefault: false
+    version: 1
+    editable: false