feat: CREATE/ALTER/DROP VIEW and MACRO in DuckLake catalog

[qsliu2017]

Parent: #124

Summary

Upstream ducklake stores views and macros (UDFs) in the DuckLake catalog with full snapshot tracking. pg_ducklake should support creating, altering, and dropping these objects with metadata synced to DuckLake.

Features

Views

• CREATE VIEW -- store view SQL definition in DuckLake metadata
• ALTER VIEW -- modify view definition
• DROP VIEW -- remove view from DuckLake metadata
• Views should participate in snapshot versioning (time-travel queryable)

Macros (UDFs)

• CREATE MACRO (scalar macros) -- store macro definition in DuckLake catalog
• CREATE MACRO (table macros) -- store table macro definition
• DROP MACRO -- remove macro from DuckLake catalog

Implementation notes

• Requires new event trigger handlers for VIEW and MACRO DDL events
• Views in DuckLake are stored as SQL text in metadata, not as PG views
• Need to decide: should these also create corresponding PG views/functions, or only exist in the DuckLake catalog?
• Related: feat: materialized view using ducklake #25 (materialized views)