feat: Adds docker metrics to prometheus scraping

Not working because custom networks (`monitoring`) cannot access use `host-gateway` to access the host machine: docker/for-linux#264 (comment) Solving requires attaching to default bridge network or doing some janky iptables stuff...

docker/docker-compose.yaml

@@ -113,6 +113,8 @@ services:
     restart: unless-stopped
     networks:
       - monitoring
+    extra_hosts:
+      - host.docker.internal:host-gateway
     volumes:
       - ./prometheus:/etc/prometheus
       - prometheus_data:/prometheus

docker/prometheus/prometheus.yml

@@ -28,8 +28,7 @@ scrape_configs:
   #     # CREATE MANUALLY: Long-Lived Access Token
   #     credentials_file: "/etc/prometheus/homeassistant-credentials.txt"
 
-# remote_write:
-#   - url: '<Your Prometheus remote_write endpoint>'
-#     basic_auth:
-#       username: '<Your Grafana Username>'
-#       password: '<Your Grafana API key>'
+  # See Ansible playbook for setup
+  - job_name: docker
+    static_configs:
+      - targets: ['host.docker.internal:9323']