Fix config schema and config options storage

    display_options:
      display_extenders:
        views_merge_rows: {  }
        metatag_display_extender:
          metatags:
            title: aaaaa
            description: bbbb
      path: aaaaa
      menu:
        type: normal
        title: aaaaa
        menu_name: main
      merge_rows: 0
      use_grouping: 0
      field_config:
        title:
          merge_option: merge
          exclude_first: 1
          prefix: mmmm
          separator: ', '
          suffix: bbbb
        changed:
          merge_option: merge_unique
          exclude_first: 0
          prefix: ghfjghfkhk
          separator: ', '
          suffix: ollll

Views Merge Rows config is not stored correctly inside the correct display extender such as Metatag does.

Need to rewrite in depth the module configuration.