title: Function to get user_id's that had their opt-in status changed after processing of the change log
body: <p>Given a list of users with their opt-in statuses and sequential change log of opt-in status updates that is applied to user list, I am trying to write a function to get a list of all user_ids (sorted by id) that had their opt-in status changed after processing of the change log</p>
  <p>Sample Input:</p>
  <pre><code>        current_user_list: [
              User({
                  id: 1,
                  opted_in: false
              }),
              User({
                  id: 19,
                  opted_in: true
              }),
              User({
                  id: 4,
                  opted_in: true
              }),
              User({
                  id: 54,
                  opted_in: false
              })
          ]
  
          opt_in_change_log: [
              OptInChange({
                  user_id: 19,
                  action: 'opt_out'
              }),
              OptInChange({
                  user_id: 1,
                  action: 'opt_in'
              }),
              OptInChange({
                  user_id: 71,
                  action: 'opt_in'
              }),
              OptInChange({
                  user_id: 19,
                  action: 'opt_in'
              })
          ]
  </code></pre>
  <p>Sample Output</p>
  <pre><code>[ 1, 71 ]
  </code></pre>
  <p>My function takes two parameters, but I am not entirely sure how to extract user_id who had their opt-in changed</p>
  <pre><code>def find_users_with_opt_change(current_user_list, opt_in_change_log):
  
  </code></pre>
  <p>EDIT: users not stored in user list are considered opted_out</p>