[docs] Sync procedure documentation

[huangxiaopingRD]

Purpose

• Remove the obsolete Flink migrate_iceberg_table procedure documentation.
• Add missing Spark/Flink procedure documentation, including repair_earliest_snapshot and several registered Flink procedures.

Tests

• The changes are documentation-only.

[JingsongLi]

The documentation for the newly added copy_files procedure fails to mention that it is deprecated and applicable only to FileSystemCatalog; furthermore, it does not produce a standard catalog snapshot, making it prone to user misuse.

[huangxiaopingRD]

The documentation for the newly added copy_files procedure fails to mention that it is deprecated and applicable only to FileSystemCatalog; furthermore, it does not produce a standard catalog snapshot, making it prone to user misuse.

Thank you for pointing it out, it has been updated.