Creator id fix

[JeroenJRP]

Description

When the creator url is different from the identity url, the references to the creator entity would be wrong.
Truncated example:

{
      "@type": "WebSite",
      "author": {
        "@id": "https://example.com#identity"
      },
      "copyrightHolder": {
        "@id": "https://example.com#identity"
      },
      "creator": {
        "@id": "https://example.com#creator"
      },
      "publisher": {
        "@id": "https://example.com#creator"
      },
      "url": "https://example.com"
},
{
      "@id": "https://example.com#identity",
      "@type": "Organization",
      "name": "Example",
      "url": "https://example.com"
},
{
      "@id": "https://onstuimig.nl#creator",
      "@type": "Organization",
      "name": "Onstuimig",
      "url": "https://onstuimig.nl"
},

This PR makes sure all references to #creator use the creator url

[khalwat]

Thank you for the PR, I will port it to the Craft 3 & Craft 5 versions of the plugin!