ARR: Let assigned SACs/ACs add or remove the authors from the comment invitation

[melisabok]

When reviews are late, the SAC/AC can add the authors so they can reply to the reviews. We would need to do the following:

• Create an invitation to edit the comment invitation readers and invitees
• The UI that shows the invitation info should render this as a button
• The SAC/AC console should render a link to the invitation UI
• Question: what happens when the PCs change the comment stage? do we overwrite the SAC/AC changes?