Workspace admins should be able to include a link to CoC in notifications

[billglover]

Workspace admins may want to include a reference or link to their Code of Conduct in notifications to users whose messages have been flagged. Because the Code of Conduct is a property of the workspace, BuddyBot should allow workspace administrators to provide a link that can be included in notifications.

This functionality must:

• notify the admins when the Code of Conduct reference is changed
• prevent non-admins from changing the Code of Conduct reference
• persist the Code of Conduct reference once it has been changed
• include the reference in the notification to users whose messages have been flagged