DBZ-5071 Correctly handle NULL values in incremental snapshots

[james-johnston-thumbtack]

This makes changes in the Db2 connector for the corresponding commit in the main Debezium project. The main thing we have to do is override the nullsSortLast function in Db2Connection to define how NULLs sort in Db2. We also have to update the test suite, since the base test suite now includes additional tests for working with keys that are nullable.

Related pull request: debezium/debezium#5158

[james-johnston-thumbtack]

I ran the following command to test:

admin@ip-10-4-98-175:~/Thumbtack/debezium-connector-db2$ mvn clean install -Dit.test=IncrementalSnapshotIT

The tests pass.

I attached the full log if you are interested.
Db2Test.log

[james-johnston-thumbtack]

From CI:

Error:    IncrementalSnapshotIT>AbstractIncrementalSnapshotTest.snapshotWithAdditionalCondition:811->AbstractSnapshotTest.consumeRecordsMixedWithIncrementalSnapshot:251->AbstractSnapshotTest.consumeMixedWithIncrementalSnapshot:182->AbstractSnapshotTest.consumeMixedWithIncrementalSnapshot:192->AbstractSnapshotTest.consumeMixedWithIncrementalSnapshot:211 [Too many no data record results, 0 < 10] 
Expecting:
 <6>
to be less than or equal to:
 <5> 

However, when I had tested the test, it passed - from the log that I posted:

2024-01-27 04:09:09,862 INFO   IncrementalSnapshotIT||test  Test io.debezium.connector.db2.IncrementalSnapshotIT#snapshotWithAdditionalCondition succeeded   [io.debezium.connector.db2.IncrementalSnapshotIT]

I'm assuming this is a previously-flaky test / unrelated to this PR...

There were also some other test failures in totally different test suites, again which seem unrelated:

Error:  Failures: 
Error:    Db2OnlineDefaultValueIT>AbstractDb2DefaultValueIT.shouldHandleDateTimeDefaultTypes:203->AbstractDb2DefaultValueIT.shouldHandleDefaultValuesCommon:217->AbstractDb2DefaultValueIT.testDefaultValuesAlterTableAdd:493->AbstractDb2DefaultValueIT.assertSchemaFieldWithDefaultCurrentDate:544->AbstractDb2DefaultValueIT.assertSchemaFieldValueWithDefault:540->AbstractDb2DefaultValueIT.lambda$assertSchemaFieldWithDefaultCurrentDate$2:552 [Unexpected field value: AVAL_DATE_SYSDATE_NONNULL] 
Expecting:
 <-719162>
to be greater than or equal to:
 <1> 

and

Error:  Errors: 
Error:  io.debezium.connector.db2.Db2ReselectColumnsProcessorIT.testNoColumnsReselectedWhenNullAndUnavailableColumnsAreDisabled
Error:    Run 1: Db2ReselectColumnsProcessorIT.beforeEach:32->AbstractReselectProcessorTest.beforeEach:60->createTable:85 » SQL ASNCAP server did not start.
Error:    Run 2: Db2ReselectColumnsProcessorIT.afterEach:41 » SqlSyntaxError DB2 SQL Error: SQLCODE=-204, SQLSTATE=42704, SQLERRMC=DB2INST1.DBZ4321, DRIVER=4.26.14