Add PQERRORS_SQLSTATE enum to type Verbosity

[taimoorzaeem]

Reopening this after previous unintentional merge which was reverted

PostgreSQL supports PQERRORS_SQLSTATE (see PGVerbosity) value for error verbosity. This is missing in the current Verbosity type. This is required for implementing PostgREST/postgrest#4088 (comment).

In libpq this was added in the following commit and here is the discussion. I am still not sure what version of libpq this was released in.

[taimoorzaeem]

In libpq this was added in the following commit and [...]

I checkout this commit and at that time the major version was 12, so at max it should be released in version 13. So, it doesn't seem like breaking change.