feat: Support DEFAULT NEXTVAL for Sequences

[BohuTANG]

Summary

Add support for using sequences as DEFAULT values in table definitions:

CREATE SEQUENCE user_id_seq;

CREATE TABLE users (
  id INT DEFAULT NEXTVAL(user_id_seq),
  name VARCHAR
);

Current Workaround

Currently requires explicit NEXTVAL in every INSERT:

INSERT INTO users VALUES (NEXTVAL(user_id_seq), 'John');