Fixes #6

Here is proposal for exposing schema metatags. I split base metatags and schema metatags into two fields, because it's easier to manage that on frontend part too.

To query schema metatags, I just add field for entity:

schema_metatags: entitySchemaMetatags {
        key
        content
}

and after that map values to object like this:

<script type="application/ld+json">
  {JSON.stringify({
    '@context': 'https://schema.org',
    '@graph': [
      schema_metatags.reduce((res, entry) => {
        res[entry.key] = JSON.parse(entry.content);
        return res;
      }, {}),
    ],
  })}
</script>

And that's it.

Bad part is, that content is encoded json, but I would like to avoid too much nesting.