[spark] Disable create table in default db

[junmuz]

Purpose

• Add a new SparkCatalog option disable-create-table-in-default-db (default false) that, when enabled, prevents the default database from being auto-created during catalog initialization and blocks CREATE TABLE statements targeting the default database. This is similar to FlinkCatalogOption
• Works with both the standard default database and custom default databases configured via defaultDatabase

Tests

• testDisableCreateTableInDefaultDb — verifies CREATE TABLE in default is rejected; creating databases and tables in non-default namespaces still works; inserted data is readable
• testDisableCreateTableWithCustomDefaultDb — verifies the guard works when defaultDatabase is set to a custom value
• testDefaultDatabaseNotCreatedWhenDisabled — verifies the default database is not auto-created during catalog initialization

[JingsongLi]

+1