Switch to PromEx for prometheus metrics

Recommending use of the separate HTTP server for exposing the metrics
and securing it externally on your firewall or reverse proxy. It will
listen on port 4021 by default.

config/config.exs

@@ -648,12 +648,26 @@ config :pleroma, Pleroma.Emails.UserEmail,
 
 config :pleroma, Pleroma.Emails.NewUsersDigestEmail, enabled: false
 
-config :prometheus, Pleroma.Web.Endpoint.MetricsExporter,
-  enabled: false,
-  auth: false,
-  ip_whitelist: [],
-  path: "/api/pleroma/app_metrics",
-  format: :text
+config :pleroma, Pleroma.PromEx,
+  disabled: false,
+  manual_metrics_start_delay: :no_delay,
+  drop_metrics_groups: [],
+  grafana: [
+    host: System.get_env("GRAFANA_HOST", "http://localhost:3000"),
+    auth_token: System.get_env("GRAFANA_TOKEN"),
+    upload_dashboards_on_start: false,
+    folder_name: "BEAM",
+    annotate_app_lifecycle: true
+  ],
+  metrics_server: [
+    port: 4021,
+    path: "/metrics",
+    protocol: :http,
+    pool_size: 5,
+    cowboy_opts: [],
+    auth_strategy: :none
+  ],
+  datasource: "Prometheus"
 
 config :pleroma, Pleroma.ScheduledActivity,
   daily_user_limit: 25,