Add config to automatically generate only the dimensionsSplitOrder in star tree

Currently, we can specify enableDefaultStarTree=True, which will create a default star tree. It will automatically generate the dimensionsSplitOrder by taking the dimension columns and sorting them by cardinality in descending order. It also contains some default pre-aggregations and a maxLeafRecords.

But we can't add more pre-aggregations to the default config.
It would be useful if we can add a config to only generate the dimensionsSplitOrder in descending order, and be able to manually specify the other parts.

@Jackie-Jiang

Start by tracing the existing enableDefaultStarTree configuration and the code that derives dimensionsSplitOrder from dimension cardinalities. Define the configuration behavior so only dimensionsSplitOrder is generated automatically while pre-aggregations and maxLeafRecords remain manually configurable; verify the existing star-tree configuration tests and add coverage for this combination.

Written by the indexing model from the issue text.