fix: updated_at set to null on insert

before it was being set to current_timestamp which was a bug

src/main/resources/db/migration/V003__fix_updated_at_insert_trigger.sql

@@ -0,0 +1,35 @@
+--- Dropping trigger to prevent them from being called while migrating data
+drop trigger if exists handle_message_timestamps on message;
+
+--- Migrate data
+update message
+set updated_at = null
+where created_at = updated_at
+  and updated_at is not null;
+
+--- Replace trigger handler
+create or replace function handle_timestamps()
+    returns trigger as
+$$
+begin
+    if lower(tg_op) = 'insert' then
+        new.created_at = coalesce(new.created_at, current_timestamp);
+        new.updated_at = null;
+    elsif lower(tg_op) = 'update' then
+        if new.created_at is distinct from old.created_at then
+            raise exception 'Direct modification of created_at is not allowed.';
+        end if;
+
+        new.updated_at = current_timestamp;
+    end if;
+
+    return new;
+end;
+$$ language plpgsql;
+
+--- Reinsert trigger
+create trigger handle_message_timestamps
+    before insert or update
+    on message
+    for each row
+execute function handle_timestamps();