Remove todo about GUID field on the 'aggregator_item' entity and add UUID field
>>> [!note] Migrated issue
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<!-- Migrated from issue #2149851. -->
Reported by: [amateescu](https://www.drupal.org/user/729614)
>>>
<p>We usually have a UUID field on each entity type using the 'uuid' field type, but aggregator items have a GUID 'string' field instead. We should convert and rename it to be in line with the rest of core.</p>
issue