plpgsql: error codes for RAISE statement doesn't match postgres

There are a few minor differences between the SQLSTATE codes returned by CRDB vs postgres (set to verbose) for the following proc:
```
CREATE PROCEDURE foo() LANGUAGE PLpgSQL AS $$
BEGIN
RAISE DEBUG 'foo';
RAISE LOG 'foo';
RAISE INFO 'foo';
RAISE NOTICE 'foo';
RAISE WARNING 'foo';
END
$$;
```
CRDB:
```
root@localhost:26257/defaultdb> CALL foo();
INFO: foo
SQLSTATE: 00000
NOTICE: foo
WARNING: foo
SQLSTATE: 00000
CALL
```
postgres:
```
postgres=# CALL foo();
INFO: 00000: foo
LOCATION: exec_stmt_raise, pl_exec.c:3883
NOTICE: 00000: foo
LOCATION: exec_stmt_raise, pl_exec.c:3883
WARNING: 01000: foo
LOCATION: exec_stmt_raise, pl_exec.c:3883
CALL
```
Postgres prints the "success" code for NOTICE, while CRDB doesn't. Also, postgres uses the 01000 "warning" code for the WARNING log level, while CRDB still uses the 00000 "success" code.

Jira issue: CRDB-33623