fix: PG CDC failed when encountering changes in PK and UK during the pullback

[caiq1nyu]

fix issues such as the following scenarios:

// source
CREATE TABLE sgiprod.ggbridgeritem (
    bridgeritemid    varchar(21) NOT NULL,
    entitytype       varchar(10),
    entityno         varchar(100),

    CONSTRAINT ggbridgeritem_pkey PRIMARY KEY (bridgeritemid),
    CONSTRAINT uk_ggbridgeritem_businesstype_no UNIQUE (entitytype, entityno)
);

-- LSN: 0001
INSERT INTO fortest.test1 VALUES ('PK1','A','NO1');
INSERT INTO fortest.test1 VALUES ('PK2','B','NO2');
UPDATE fortest.test1 SET entitytype='C', entityno='TEMP' where bridgeritemid='PK1'; 
UPDATE fortest.test1 SET entitytype='A', entityno='NO1' where bridgeritemid='PK2';
UPDATE fortest.test1 SET entitytype='B', entityno='NO2' where bridgeritemid='PK1';
-- LSN: 0002

// target
-- The data is in LSN:0002 state, and CDC is pulled back to LSN:0001.
-- origin sql will be like:
INSERT INTO fortest.test1 VALUES ('PK1','LOG1','A','NO1') ON CONFLICT(bridgeritemid) UPDATE SET entitytype='A', entityno='NO1';
-- which will cause duplicate key value violates unique constraint error

In the current design, this scenario is likely to occur when performing a full load plus an incremental load. This PR will fix it.