Add NOT-NULL Constraint on (p_)ci_builds on project

https://docs.gitlab.com/ee/development/database/not_null_constraints.html#add-a-not-null-constraint-to-an-existing-column

We need to fix ci_builds and p_ci_builds to not allow null project values. This will enable sharding and unblock other tables that only have association to p_ci_builds and ci_builds