Inconsistent behavior between SQL and DataFrame API on store assignment policy

[Manu Zhang]

Hi community,

With `spark.sql.storeAssignmentPolicy=LEGACY` in Spark 3.5, it's not
allowed to write to DSv2 with insert SQL. However, this can be worked
around with DataFrame API, i.e., `df.writeTo($dsv2Table).append()`

Is this expected?

Thanks,
Manu