1. Simplify the use of flink connector like other stream sink by GenericDorisSinkFunction.
2. Add the use cases of flink connector.
## Use case
```
env.fromElements("{\"longitude\": \"116.405419\", \"city\": \"北京\", \"latitude\": \"39.916927\"}")
.addSink(
DorisSink.sink(
DorisOptions.builder()
.setFenodes("FE_IP:8030")
.setTableIdentifier("db.table")
.setUsername("root")
.setPassword("").build()
));
```