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.

spec/components/admin/stats/global_chart_component_spec.rb

@@ -0,0 +1,18 @@
+require "rails_helper"
+
+describe Admin::Stats::GlobalChartComponent do
+  before do
+    allow(Ahoy::Chart).to receive(:active_event_names).and_return(
+      %i[budget_investment_created level_3_user]
+    )
+  end
+
+  it "renders an <h2> tag with a graph and links" do
+    render_inline Admin::Stats::GlobalChartComponent.new
+
+    expect(page).to have_css "h2", exact_text: "Graphs"
+    expect(page).to have_css "[data-graph]"
+    expect(page).to have_link "Budget investments created"
+    expect(page).to have_link "Level 3 users verified"
+  end
+end