Separate table as a project settings key/value store

The following discussion from !13923 (merged) should be addressed:

• @grzesiek started a discussion: (+2 comments)

  It feels like we keep every project settings inside projects table, as a boolean column, which is not the perfect solution of course. I wonder if we need projects_settings table with a key/value store or something like this. Nevertheless is might be out of scope for this MR indeed.