[server] Support altering auto partition num-precreate option

[fhan688]

Purpose

Linked issue: #3351

This PR allows table.auto-partition.num-precreate to be altered dynamically after table creation.

Before this change, auto partition retention could be updated by ALTER TABLE, but table.auto-partition.num-precreate was rejected by alter table validation. This PR enables users to increase or decrease the number of pre-
created auto partitions without recreating the table.

Brief change log

• Add table.auto-partition.num-precreate to alterable Fluss table options.
• Refresh AutoPartitionManager when either num-retention or num-precreate changes.
• When num-precreate is increased, missing future partitions are created after the table property change is observed.
• When num-precreate is decreased, existing pre-created partitions are kept, and future auto partition runs stop over-creating partitions.
• Add server-side coverage for updating num-precreate.
• Add Flink catalog IT coverage for ALTER TABLE SET/RESET ('table.auto-partition.num-precreate' ...).
• Update docs for Flink DDL/options and partitioning behavior.

Tests

• AutoPartitionManagerTest#testUpdateAutoPartitionNumPrecreate
• Flink120CatalogITCase#testAlterAutoPartitionNumPrecreate
• git diff --check

API and Format

This change does not modify RPC protocol, storage format, or serialized metadata format.

It expands the supported dynamic table property set by allowing table.auto-partition.num-precreate to be changed through ALTER TABLE SET and reset through ALTER TABLE RESET.

Documentation

Updated documentation:

• website/docs/engine-flink/ddl.md
• website/docs/engine-flink/options.md
• website/docs/table-design/data-distribution/partitioning.md