GH-519 - Improve Postgres default indexes.

We now use a hash index for the serialized event to improve performance.

spring-modulith-events/spring-modulith-events-jdbc/src/main/resources/schema-postgresql.sql

@@ -8,5 +8,5 @@ CREATE TABLE IF NOT EXISTS event_publication
   completion_date  TIMESTAMP WITH TIME ZONE,
   PRIMARY KEY (id)
 );
-CREATE INDEX IF NOT EXISTS event_publication_by_listener_id_and_serialized_event_idx ON event_publication (listener_id, serialized_event);
+CREATE INDEX IF NOT EXISTS event_publication_serialized_event_hash_idx ON event_publication USING hash(serialized_event);
 CREATE INDEX IF NOT EXISTS event_publication_by_completion_date_idx ON event_publication (completion_date);