fix(policy): return fqns in list subject mappings (#1796)

### Proposed Changes

* returns mapped attribute value FQNs in `ListSubjectMappings` as FQNs
provide the namespace and definition of the attribute value

### Checklist

- [ ] I have added or updated unit tests
- [ ] I have added or updated integration tests (if appropriate)
- [ ] I have added or updated documentation

### Testing Instructions

Author: jakedoublev

service/integration/subject_mappings_test.go

@@ -404,14 +404,17 @@ func (s *SubjectMappingsSuite) Test_ListSubjectMappings_NoPagination_Succeeds()
 	for _, sm := range listed {
 		if sm.GetId() == fixture1.ID {
 			assertEqual(sm, fixture1)
+			s.Equal("https://example.com/attr/attr1/value/value1", sm.GetAttributeValue().GetFqn())
 			found1 = true
 		}
 		if sm.GetId() == fixture2.ID {
 			assertEqual(sm, fixture2)
+			s.Equal("https://example.com/attr/attr1/value/value2", sm.GetAttributeValue().GetFqn())
 			found2 = true
 		}
 		if sm.GetId() == fixture3.ID {
 			assertEqual(sm, fixture3)
+			s.Equal("https://example.com/attr/attr1/value/value1", sm.GetAttributeValue().GetFqn())
 			found3 = true
 		}
 	}

service/policy/db/query.sql

@@ -839,13 +839,19 @@ SELECT
         'metadata', JSON_STRIP_NULLS(JSON_BUILD_OBJECT('labels', scs.metadata->'labels', 'created_at', scs.created_at, 'updated_at', scs.updated_at)),
         'subject_sets', scs.condition
     ) AS subject_condition_set,
-    JSON_BUILD_OBJECT('id', av.id,'value', av.value,'active', av.active) AS attribute_value,
+    JSON_BUILD_OBJECT(
+        'id', av.id,
+        'value', av.value,
+        'active', av.active,
+        'fqn', fqns.fqn
+    ) AS attribute_value,
     counted.total
 FROM subject_mappings sm
 CROSS JOIN counted
 LEFT JOIN attribute_values av ON sm.attribute_value_id = av.id
+LEFT JOIN attribute_fqns fqns ON av.id = fqns.value_id
 LEFT JOIN subject_condition_set scs ON scs.id = sm.subject_condition_set_id
-GROUP BY av.id, sm.id, scs.id, counted.total
+GROUP BY av.id, sm.id, scs.id, counted.total, fqns.fqn
 LIMIT @limit_
 OFFSET @offset_;