[improvement]Add an option to set the partition size of the final write stage

[lexluo09]

Proposed changes

Add an option to set the partition size of the final write stage

1. We can increase the parallelism of the computation and reduce the write doris parallelism to reduce write compaction pressure.
2. After the spark RDD is filtered, the number of records for each partition is small and the number of partitions is large. The writing frequency becomes high and resources are wasted.

Problem Summary:

Describe the overview of changes.

Checklist(Required)

1. Does it affect the original behavior: (Yes/No/I Don't know)
2. Has unit tests been added: (Yes/No/No Need)
3. Has document been added or modified: (Yes/No/No Need)
4. Does it need to update dependencies: (Yes/No)
5. Are there any changes that cannot be rolled back: (Yes/No)

Further comments

before :

after :

[lexluo09]

@hf200012 would you mind take a look?

[gnehil]

LGTM, and please update the docs on the official website to explain that doris.sink.task.partition.size is required, and the difference between setting doris.sink.task.use.repartition to true or false.

[hf200012]

LGTM

[lexluo09]

LGTM, and please update the docs on the official website to explain that doris.sink.task.partition.size is required, and the difference between setting doris.sink.task.use.repartition to true or false.

Ok, thank you very much for your advice