Fix harvest_source notification_emails field

[btylerburton]

When creating/editing a harvest source in datagov-harvest-admin, and entering an email into the notification_emails text area, the email is split up into individual characters.

How to reproduce

1. Create/edit a harvest source in datagov-harvest-admin
2. Add an email to the Notification_emails field.
3. Click Submit/Update to save the change

Expected behavior

1. Email(s) stored as a comma-separated list

Actual behavior

1. Email addresses are split up as strings and saved as an array.

ex. a@a.com -> ['a', '@', 'a', '.', 'c', 'o', 'm']

Sketch

• [ ] Create proper relationship and entity for saving emails
• [ ] Potentially employ a separate table and join them in the form

[jbrown-xentity]

@Jin-Sun-tts mentioned this is annoying, and will take on shortly.