Add watchers to an opportunity

When you select recruiters on step 6, all the recruiters added are on the extended offer, decline application, and contact applicant letters. However, only one primary recruiter should be on those letters, and those other recruiters are only watchers or supporters of the volunteer opportunity and not actively recruiting. Adding a watcher's field allows you to add multiple people to monitor the opportunity. Then, we can remove them from the select recruiters listed in the letters.