feat: Public comments in shared documents

Expected Behavior

As proposed in https://github.com/outline/outline/issues/7362#issuecomment-4439043821, the proposal is that anonymous users can add comments to shared documents.

Here are proposed changes:

1. Additional switch that a shared document can have public comments in share settings

1. When writing comments in the document internally there would be additional switch if the document should be internal or visible in shared view

1. On the shared document view, there would be same comments functionality as in internal view

1. Once the comment is sent, a dialog appears for guest name and email

I am working on a working prototype that could be later used as bases for a PR