Add a chart showing all events in admin stats

Not sure it's useful, but it makes the main admin stats page a bit more
interesting.

app/components/admin/stats/global_chart_component.rb

@@ -0,0 +1,19 @@
+class Admin::Stats::GlobalChartComponent < ApplicationComponent
+  private
+
+    def event_names
+      Ahoy::Chart.active_event_names
+    end
+
+    def chart_tag
+      tag.div("data-graph": data_points.to_json)
+    end
+
+    def data_points
+      Ahoy::Chart.active_events_data_points
+    end
+
+    def title
+      t("admin.stats.graph.title")
+    end
+end