Add facet/filter for 'related'

[jamieu]

So that we can filter by objects related to a specific person or company ie. https://collection.sciencemuseumgroup.org.uk/search/objects/related/***

Related people

https://collection.sciencemuseumgroup.org.uk/api/objects/co27893/seaforth-sands-station-model-station

"relationships": {
      "people": { "data": [ { "type": "people", "id": "cp89483" } ] },
      "terms": {
        "data": [
          { "type": "term", "id": "ct266653" },
          { "type": "term", "id": "ct266633" }
        ]
      }
    }

"included": [
    {
      "type": "people",
      "id": "cp89483",
      "attributes": {
        "role": { "value": "sitter" },
        "summary_title": "Liverpool Overhead Railway Company"
      },
      "links": {
        "self": "https://collection.sciencemuseumgroup.org.uk/people/cp89483/liverpool-overhead-railway-company"
      }
    }
  ],

Maker

https://collection.sciencemuseumgroup.org.uk/api/objects/co192230/boxed-bottle-of-interferon-london-england-1981-interferon

    "relationships": {
      "places": { "data": [ { "type": "place", "id": "cd113" } ] },
      "terms": {
        "data": [
          { "type": "term", "id": "ct264967" },
        ]
      },
      "maker": { "data": [ { "type": "people", "id": "cp111522" } ] }
    }

 "included": [
    {
      "type": "people",
      "id": "cp111522",
      "attributes": {
        "role": { "type": "maker", "value": "maker" },
        "summary_title": "The Wellcome Foundation Limited"
      },
      "links": {
        "self": "https://collection.sciencemuseumgroup.org.uk/people/cp111522/the-wellcome-foundation-limited"
      }
    }
  ],