Create the project_settings table

I'm creating this issue to create awareness of #19826 (closed)

I see quite regularly MRs are adding more fields to the projects table (for example !18408 (merged)), so it would be nice if someone of the database team to work on migrating field to a separate projects_settings table.

As a start, we should create the table, and have at least new MRs trying to add fields to projects add the fields to project_settings instead of projects, so we stop creating more maintenancerefactor in GitLab.org / Database Team / team-tasks.