Add groups index page

When render the investment list component with the link "see all
investments", now we redirect to groups index page when a budget has
multiple headings.

app/components/budgets/groups/index_component.html.erb

@@ -0,0 +1,8 @@
+<% content_for :canonical do %>
+  <%= render "shared/canonical", href: budget_groups_url %>
+<% end %>
+
+<main class="budget-groups-index">
+  <%= header(before: back_link_to(budget_path(budget))) %>
+  <%= render Budgets::GroupsAndHeadingsComponent.new(budget) %>
+</main>

app/components/budgets/groups/index_component.rb

@@ -0,0 +1,12 @@
+class Budgets::Groups::IndexComponent < ApplicationComponent
+  include Header
+  attr_reader :budget
+
+  def initialize(budget)
+    @budget = budget
+  end
+
+  def title
+    t("budgets.groups.show.title")
+  end
+end

app/components/budgets/investments_list_component.html.erb

@@ -14,7 +14,7 @@
   <div class="row margin-top">
     <div class="small-12 medium-6 large-4 small-centered column margin-top">
       <%= link_to t("budgets.investments_list.see_all"),
-                  budget_investments_path(budget),
+                  see_all_path,
                   class: "button expanded" %>
     </div>
   </div>

app/components/budgets/investments_list_component.rb

@@ -17,4 +17,12 @@ class Budgets::InvestmentsListComponent < ApplicationComponent
       budget.investments.none
     end
   end
+
+  def see_all_path
+    if budget.single_heading?
+      budget_investments_path(budget)
+    else
+      budget_groups_path(budget)
+    end
+  end
 end

app/components/concerns/header.rb

@@ -1,7 +1,7 @@
 module Header
   extend ActiveSupport::Concern
 
-  def header(&block)
+  def header(before: nil, &block)
     provide(:title) do
       [
         t("#{namespace}.header.title", default: ""),
@@ -17,11 +17,7 @@ module Header
                   end
 
     tag.header do
-      if block_given?
-        content_tag(heading_tag, title) + capture(&block)
-      else
-        content_tag(heading_tag, title)
-      end
+      safe_join([before, content_tag(heading_tag, title), (capture(&block) if block_given?)].compact)
     end
   end