Allow optionGroups/options to be sortable

[dlhck]

Migrated from #865

We have introduced variants to our products. Currently we are unable to sort the optionGroups or the options within them. This is a problem for when one wants to build dropdowns with intuitive order e.g. "Size" dropdown before "Colour".

Furthermore within the optionGroups you want to be able to order "Small" before "Large". As a workaround we have had to duplicate data of the optionGroups within the frontend, which is undesirable as it complicates product management and increases risk. GraphQl output below:

Example fo current graphQL output:

"optionGroups": [
        {
          "options": [
            {
              "group": {
                "name": "Size"
              },
              "name": "Large"
            },
            {
              "group": {
                "name": "Size"
              },
              "name": "Small"
            }
          ]
        },
        {
          "options": [
            {
              "group": {
                "name": "Wine"
              },
              "name": "+ with Wine"
            },
            {
              "group": {
                "name": "Wine"
              },
              "name": "- without Wine"
            }
          ]
        }
      ],