Row Comments MR 1/4 - Backend Only without realtime and comment counts

Merge Request Checklist

• changelog.md has been updated if required
• Documentation has been updated
• Quality Standards are met
• The UI/UX has been updated following UI Style Guide
• The redoc API pages have been updated for any REST API changes
• The per database user API docs page has been updated for any REST API changes made to endpoints which can be accessed via a user created token
• Has performance been considered and tested when appropriate? Ideally Baserow should be performant when working with hundreds of thousands of rows
• New/Changed Premium features are separated correctly in the premium folder

This MR is the first one as detailed in https://gitlab.com/bramw/baserow/-/issues/539#note_635514571 and soley adds the backend endpoints for row comments without realtime, the frontend and also doesn't include per row comment counts.

Testing Notes

• Can manually create and get row comments using a rest client
• New prem migration works fine on startup
• Can still delete/restore the row and see the row comments also restored
• When a row is trashed the endpoint returns 404
• Perm deleting a row with comments works fine
• Can still do basic Baserow things like edit/create rows.
• Can still access other premium parts of the site.