Migrate MR-related Project settings off projects table

We have Project-level settings scattered across 2 tables - projects and project_settings. projects is a really wide table with many, many rows; maybe we should think about migrating and consolidating them into either project_settings or create a series of tables for each major section. This would benefit projects itself, and give us an excuse and opportunity to take a pass at documenting and rationalizing the values of these columns; boolean in nature, we have inconsistencies in whether, say, a value of true is enabling or disabling of that setting.. it has tripped us up in the past.

This work, if we were to take it on, should be done in consult with devopsmanage and devopsplan, both of whom have project-level settings of their own.

Initial discussion: #344632 (comment 958851466)