The interface for converter to ClickHouse format

[mchernyakov]

@aleksanchezz @ashulenko
Probably, for more obvious using this sink we should add the cpecific interface, something like this:

public interface ClickHouseSinkConverter<T> {
  String convert(T record);
}

And we can use it directly in the sink:

ClickHouseSinkConverter<SomeClass> chConverter = ....;
DataStream<YourEvent> dataStream = ...;
dataStream.addSink(new ClickhouseSink(props, chConverter))
                   .name("your_table clickhouse sink);

And inside https://github.com/ivi-ru/flink-clickhouse-sink/blob/master/src/main/java/ru/ivi/opensource/flinkclickhousesink/ClickhouseSink.java#L53 .

[spancer]

That should be really helpful, if a converter is supported.

[mchernyakov]

@spancer hi, it is not a converter, it is just an interface. Basically, this ticket is about refactoring.

It's quite tricky to implement an universal converter from Java Object to Clickhouse-format String. But if you have some will, you could try.

Contributions are welcome.

[mchernyakov]

implemented in #22