Fix "rel" attribute in footer description links

We were accidentally filtering this attribute when sanitizing the text
since commit 928312e21.

app/components/layout/footer_component.html.erb

@@ -8,7 +8,8 @@
       <p class="info">
         <%= sanitize(t("layouts.footer.description",
                        open_source: open_source_link,
-                       consul: repository_link)) %>
+                       consul: repository_link),
+                     attributes: allowed_link_attributes) %>
       </p>
     </div>
 

app/components/layout/footer_component.rb

@@ -14,4 +14,8 @@ class Layout::FooterComponent < ApplicationComponent
     def repository_link
       link_to(t("layouts.footer.consul"), t("layouts.footer.consul_url"), rel: "nofollow")
     end
+
+    def allowed_link_attributes
+      self.class.sanitized_allowed_attributes + ["rel"]
+    end
 end

spec/components/layout/footer_component_spec.rb

@@ -6,6 +6,7 @@ describe Layout::FooterComponent do
       render_inline Layout::FooterComponent.new
 
       page.find(".info") do |info|
+        expect(info).to have_css "a[rel=nofollow]", count: 2
         expect(info).not_to have_css "a[target]"
       end
     end