feat: add postgres/gitea/blackbox alerts and more node alerts

environments/dev/adibrov/alerts/postgres/postgres_down.yaml

@@ -0,0 +1,19 @@
+name: "DEV ADIBROV - PostgreSQL Down"
+expression: |
+  pg_up{job="postgres"}
+threshold: 1
+for: "2m"
+condition_type: "lt"
+need_reduce: true
+reducer_type: "min"
+no_data_state: "Alerting"
+exec_err_state: "Alerting"
+labels:
+  service: "postgres"
+  severity: "critical"
+  team: "infra"
+summary: |
+  PostgreSQL недоступен на {{ $labels.instance }}
+description: |
+  Exporter не может подключиться к PostgreSQL на {{ $labels.instance }}.
+  База данных либо упала, либо недоступна по сети.