Add Notes field to Review Agency tasks

[adriensalz]

Support wants to streamline how we process and resolve Zendesk tickets. Because these tasks can get complicated, it's been difficult to pass them off to more than one person at a time. It's been hard to keep track of who has done what, and what progress we've made on any given task.

We may involve Zendesk tickets in the course of resolving these tasks, but Support doesn’t want to click off the site to get full context on what we’ve already tried. It also runs the risk of clogging up our Tier Two queue.

These tasks can already get long, so we'd want this to be a toggle-able option near the top of the task (or maybe a separate tab, depending on what's simpler to build.) Otherwise, this can be similar visually to the Notes option on a request page.