[spark] Introduce CTAS support for partitioned tables

[ArnavBalyan]

Purpose

• CTAS rejects all partitioned format tables even though Paimon writer supports partitioned writes.
• Allow partitioned CTAS when the Paimon writer is selected and support writing partition paths and metadata.
• Continue rejecting the Spark engine writer, which does not support partitioned format table writes in current Spark version.

Tests

• UT

[ArnavBalyan]

cc @JingsongLi @Zouxxyy thanks! :)