[SUPPORT] How to reduce the bucket number for each partition

At present, spark provides to increase bucket numbers automatically.
But in the case of partitioning, the data volume of each partition is not necessarily balanced.
The initially specified bucket number is generally calculated according to the maximum partition, resulting in too many small partitions with the same number.
It cannot reduce the bucket number of small partitions at present.

**Environment Description**

* Hudi version : 0.12.1

* Spark version : 3.1.3

* Hive version : 3.1.0

* Hadoop version : 3.1.1

* Storage (HDFS/S3/GCS..) : HDFS

* Running on Docker? (yes/no) : no

The issue provides no source files, tests, or entry points. Start by investigating how Hudi handles Spark bucket allocation for partitioned data, using the stated Hudi, Spark, Hive, Hadoop, and HDFS versions; done means smaller partitions can use fewer buckets without disrupting partitioned writes.

Written by the indexing model from the issue text.