[FLINK-26848][JDBC]Support to write data when disable flush-interval and max-rows

[hehuiyuan]

What is the purpose of the change

sink.buffer-flush.interval	The flush interval mills, over this time, asynchronous threads will flush data. Can be set to '0' to disable it. Note, 'sink.buffer-flush.max-rows' can be set to '0' with the flush interval set allowing for complete async processing of buffered actions.
sink.buffer-flush.max-rows	The max size of buffered records before flush. Can be set to zero to disable it.

Asynchronous thread flush is disabled  when set sink.buffer-flush.interval = 0,  then disable sink.buffer-flush.max-rows, which causes the data is not written out.

The data are not written when disable flush.interval and max-rows. I think it should write out when the data arrive.

[flinkbot]

CI report:

• b4cd6fa Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[hehuiyuan]

@flinkbot run azure

[hehuiyuan]

Hi @MartijnVisser @rkhachatryan, have a look when you are free.

[MartijnVisser]

@hehuiyuan I'm not a JDBC expert, so I can't review this PR.

[rkhachatryan]

Thanks for the PR @hehuiyuan , I'm also not an expert in connectors/JDBC.
@fapaul, @JingsongLi, maybe you could take a look?

[hehuiyuan]

hi @fapaul @JingsongLi , have a look this pr.

[MartijnVisser]

We've now moved the code from the JDBC connector to its own dedicated repository; please re-route this PR to https://github.com/apache/flink-connector-jdbc