refactor: Move some code that updates pg_constraint to a separate function
This extracts common/duplicate code for different ALTER CONSTRAINT
variants into a common function. We plan to add more variants that
would use the same code.
Author: Amul Sul <amul.sul@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CAAJ_b962c5AcYW9KUt_R_ER5qs3fUGbe4az-SP-vuwPS-w-AGA@mail.gmail.com