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.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