EE->CE: Move "Require code owner approval" setting from Project to ProtectedBranches

This MR is the CE-specific work (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/16187) towards the second half of backend work to address #13251 (closed), specifically migrating data from the projects table to the protected_branches table, and unwinding any cases where we inquire of the project rather than the protected_branches themselves as to whether or not "code owner approval required"

This work was originally part of !14900 (merged) (and #10395) and received some initial reviews from @tigerwnz and @abrandl.