slapos_cloud: add follow_up category on Compute Node

To attach to a project

master/bt5/slapos_cloud/PortalTypeBaseCategoryTemplateItem/base_category_list.xml

 <base_category_list>
  <portal_type id="Compute Node">
   <item>destination_section</item>
+  <item>follow_up</item>
   <item>source_administration</item>
  </portal_type>
  <portal_type id="Computer Model">

master/bt5/slapos_cloud/bt/template_portal_type_base_category_list

 Compute Node | destination_section
+Compute Node | follow_up
 Compute Node | source_administration
 Computer Model | source_administration
 Computer Network | source_administration