[migration] add_workflow now ensure the entity type is actually workflowable, and a new make_workflowable migration function is available to make an entity type workflowable (closes #1382720)

if versions_map['cubicweb'][0] == (3, 7, 4):
    config['http-session-time'] *= 60
    config['cleanup-session-time'] *= 60
    config['cleanup-anonymous-session-time'] *= 60