fix(pg): manage event triggers in SDL catalog

[rebelice]

Summary

• add catalog support for CREATE/ALTER/DROP/COMMENT ON EVENT TRIGGER
• include event triggers in SDL ordering, diff, migration generation, cloning, comments, rename, and dependency cleanup
• validate event trigger functions and command tag filters against PostgreSQL behavior, including table_rewrite tags

Verification

• go test ./pg/...
• git diff --check
• local parity check against ~/Github/postgres/src/include/tcop/cmdtaglist.h for event_trigger_ok/table_rewrite_ok