def list_section(service_name = nil, section_name = nil, graph_name = nil)
      graphs = list_graph(service_name, section_name, graph_name)
      services = {}
      graphs.each do |graph|
        service_name, section_name = graph['service_name'], graph['section_name']
        services[service_name] ||= {}
        services[service_name][section_name] ||= true
      end
      Hash[services.map {|service_name, sections| [service_name, sections.keys] }]
    end
def list_section(service_name = nil, section_name = nil, graph_name = nil)
      graphs = list_graph(service_name, section_name, graph_name)
      services = {}
      graphs.each do |graph|
        service_name, section_name = graph['service_name'], graph['section_name']
        services[service_name] ||= {}
        services[service_name][section_name] ||= true
      end
      Hash[services.map {|service_name, sections| [service_name, sections.keys] }]
    end
A Helper: Get the list of section
 @return [Hash] list of sections
 @example
 {
   "service_name1" => [
     "section_name1",
     "section_name2",
   ],
   "service_name2" => [
     "section_name1",
     "section_name2",
   ],
 }