[Perf] Enforce course code constraint in table directly

[anhgelus]

Instead of enforcing course's code constraint in libpolybase, we may add it directly in the database to avoid entering invalid data.

We can do this with:

ALTER TABLE course
ADD COLUMN code_su CHAR(7)
CHECK(code_su REGEXP '[LMU]{2}(\d)IN\d{3}');

-- copy code from course.code in course.code_su

ALTER TABLE course
DROP COLUMN code;