Added taxanomy to Graphql EntriesQuery

[SteJW]

This allows you to filter in GraphQL on the taxanomy. The basic filter function is pretty simple and doesn't allow to filter on multiple values.

How the query looks when using taxanomy.

query Entry {
  entries(collection: "products", filter: {
    taxonomy: ["target::moederfiets","target::fiets"],
  }) {
    data {
      ... on Entry_Products_Products {
        id
        title
        slug
        product_type {
          slug
          id
        }
        target {
          slug
          id
        }
      }
    }
  }
}

I tried using queries like this, but no luck. Added a quick fix at #4739 but that doesn't work correctly either.

query Entry {
  entries(collection: "products", filter: {
    target: {in: {slug : [ "fiets"]}},
  }) {
    data {
      ... on Entry_Products_Products {
        id
        title
        slug
        product_type {
          slug
          id
        }
        target {
          slug
          id
        }
      }
    }
  }
}

I copied this function from https://github.com/statamic/cms/blob/3.2/src/Tags/Collection/Entries.php:300

[jasonvarga]

With taxonomies potentially being reworked soon, I'd like to avoid adding more taxonomy features until then.

You may currently filter by taxonomy using a regular filter.

query MyQuery {
  entries(collection: "articles", filter: {
    tags: { contains: "sneakers" }
  }) {
    data {
      title
      id
    }
  }
}