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/event_links_component_spec.rb

@@ -1,12 +1,11 @@
 require "rails_helper"
 
 describe Admin::Stats::EventLinksComponent do
-  it "renders an <h2> heading followed by a list of links" do
+  it "renders a list of links" do
     render_inline Admin::Stats::EventLinksComponent.new(
       %w[legislation_annotation_created legislation_answer_created]
     )
 
-    expect(page).to have_css "h2", exact_text: "Graphs"
     expect(page).to have_link count: 2
 
     page.find("ul") do |list|