Reworking belongs_to precense validations

[urkle]

Currently a validation for a column like this

      t.belongs_to :organization, {
          null: false,
          foreign_key: {on_update: :restrict, on_delete: :cascade},
          index: true
      }

is being generated as this

[schema_validations] Project.validates_presence_of :organization

It should instead be created as this

[schema_validations] Project.validates_presence_of :organization_id

As we have an FK constraint at the DB level, thus that will enforce that a proper value will be created. This will save having to do an extra hit the DB (and loading the entire model) to validate that the org_id is a valid one.