approvals: move post approval endpoint to /post_approvals.

Move the post approval endpoint from `POST /moderator/post/approval` to
`POST /post_approvals`.

test/functional/post_approvals_controller_test.rb

@@ -3,11 +3,22 @@ require 'test_helper'
 class PostApprovalsControllerTest < ActionDispatch::IntegrationTest
   context "The post approvals controller" do
     setup do
-      @approval = FactoryBot.create(:post_approval)
+      @approver = create(:approver)
+    end
+
+    context "create action" do
+      should "render" do
+        @post = create(:post, is_pending: true)
+        post_auth post_approvals_path(post_id: @post.id, format: :js), @approver
+
+        assert_response :success
+        assert(!@post.reload.is_pending?)
+      end
     end
 
     context "index action" do
       should "render" do
+        @approval = create(:post_approval)
         get post_approvals_path
         assert_response :success
       end