Draft: Added conditional validation for complex relations

fixes https://gitlab.ruhr-uni-bochum.de/FDM/rdm-system/antleaf-projectmanagement/-/issues/187

hyrax/app/inputs/nested_relation_input.rb

@@ -16,7 +16,7 @@ protected
     field_name = name_for(attribute_name, index, field, parent)
     field_id = id_for(attribute_name, index, field, parent)
     field_value = value.send(field).first
-
+    out << "<div class='complex_relation_section'>"
     out << "<div class='row'>"
     out << "  <div class='col-md-3'>"
     out << template.label_tag(field_name, 'Title', required: required)
@@ -89,7 +89,8 @@ protected
     out << destroy_widget(attribute_name, index, field_label, parent)
     out << '  </div>'
 
-    out << '</div>' # last row
+    out << '</div>'
+    out << '</div>'
     out
   end
 end