Add to label report documentation: get verbatim agents for labels

[Jegelewicz]

left outer join (select collection_object_id,string_agg(attribute_value,'; ') as vacls from attributes 
			where attribute_type ='verbatim agent' and attribute_remark= 'collector' 
			group by collection_object_id) vac
			on coll_object.collection_object_id=vac.collection_object_id

That particular iteration works only if the documentation hasn't been followed, and joins to a bit of a weird table that most probably won't include.

ArctosDB/arctos#5449 (comment) is more portable

left outer join (
    select 
      collection_object_id,
      string_agg(attribute_value,'; ') as vacls 
    from 
      attributes 
    where 
      attribute_type ='verbatim agent' and 
      determination_method= 'collector' 
    group by 
      collection_object_id
  ) vac on flat.collection_object_id=vac.collection_object_id

Originally posted by @Jegelewicz in ArctosDB/arctos#5449 (comment)