[Query engine] Auto inject generated unique ID into omnisharded queries

[levkk]

Description

Automatically inject pgdog.unique_id() (and value) into queries that insert into omnisharded tables but don't provide the identifier value, e.g.:

INSERT INTO omnisharded (value) VALUES ('test');
-- rewrite to
INSERT INTO omnisharded (id, value) VALUES (pgdog.unique_id(), 'test');