Propagate triggers affecting distributed tables

It would be nice if triggers associated with a table were automatically propagated across all databases when the table sharding occurs. Perhaps it could be an optional flag, as I could envision scenarios where this might be undesirable.

The issue names no files, tests, or entry points. Start by locating the distributed-table sharding and trigger handling paths, then determine how trigger propagation should interact with the proposed optional flag. Done means triggers associated with a sharded table are propagated across all databases when enabled, while remaining optional.

Written by the indexing model from the issue text.