Change donations to contrbutions, add tabbed nav

Introduces components for tabbed navigation and adds a tab menu and item
for non-financial contributions to the donations/contributions page.

app/components/main_with_tabnav_component.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class MainWithTabnavComponent < ViewComponent::Base
+  def initialize(tabnav_partial:)
+    @tabnav_partial = tabnav_partial
+  end
+end