chore: Public metrics config API endpoint (#10568)

apps/block_scout_web/lib/block_scout_web/controllers/api/v2/config_controller.ex

@@ -16,4 +16,12 @@ defmodule BlockScoutWeb.API.V2.ConfigController do
     |> put_status(200)
     |> json(%{limit: limit})
   end
+
+  def public_metrics(conn, _params) do
+    public_metrics_update_period_hours = Application.get_env(:explorer, Explorer.Chain.Metrics)[:update_period_hours]
+
+    conn
+    |> put_status(200)
+    |> json(%{update_period_hours: public_metrics_update_period_hours})
+  end
 end

apps/block_scout_web/lib/block_scout_web/routers/api_router.ex

@@ -108,6 +108,7 @@ defmodule BlockScoutWeb.Routers.ApiRouter do
     scope "/config" do
       get("/backend-version", V2.ConfigController, :backend_version)
       get("/csv-export", V2.ConfigController, :csv_export)
+      get("/public-metrics", V2.ConfigController, :public_metrics)
     end
 
     scope "/transactions" do