Refactor labels management from HAML to Vue - Add `type` field to GraphQL query

We need to be able to tell the difference between ProjectLabel and GroupLabel when using the Project.labels query. We should add a type field to https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/types/label_type.rb. The type field should be an enum.

module Types
  class LabelTypeEnum < BaseEnum
    value 'PROJECT', description: 'Project label.'
    value 'GROUP', description: 'Group label.'
  end
end