fixed pictures

doc/images/flows_invoker_check_authentication.jpg

doc/images/flows_invoker_discover.jpg

doc/images/flows_invoker_get_tokens.jpg

doc/images/flows_invoker_onboard.jpg

doc/images/flows_invoker_path.jpg

doc/images/flows_invoker_update_offboard.jpg

doc/images/flows_provider_onboard.jpg

doc/images/flows_provider_path.jpg

doc/images/flows_provider_publish_functions.jpg

doc/images/flows_provider_update_offboard.jpg

doc/images/flows_updated_opencapif.jpg