Define JSON Schema $refs for linking/embedding videos and linking documents

@lauriii, do you agree that does not make sense to support, and the 3 remaining missing $refs in the issue summary would address all needs?

@lauriii, also see the issue summary: do you want only (oEmbed) remote video, or also local video URLs?

Added more detail to the oEmbed video proposal.

I think we should express the uploaded videos as follows in schema.json:

{
  "video": {
    "title": "video",
    "type": "object",
    "required": ["src"],
    "properties": {
      "src": {
        "title": "Video URL",
        "type": "string",
        "format": "uri"
      },
      "poster": {
        "title": "Poster image URL",
        "$ref": "json-schema-definitions://experience_builder.module/image-uri"
      },
      "width": {
        "title": "Video width",
        "type": "integer"
      },
      "height": {
        "title": "Video height",
        "type": "integer"
      },
      "autoplay": {
        "title": "Autoplay",
        "type": "boolean"
      },
      "loop": {
        "title": "Loop",
        "type": "boolean"
      },
      "muted": {
        "title": "Muted",
        "type": "boolean"
      },
      "controls": {
        "title": "Show controls",
        "type": "boolean"
      }
    }
  }
}

For oEmbed, I'm not sure we need the max width / max height here. It seems something that the component itself should handle? We may need to expose the height / width of the resource, as well as title which would make this shape as follows in schema.json:

{
  "oembed_video": {
    "title": "oembed_video",
    "type": "object",
    "required": ["url"],
    "properties": {
      "url": {
        "title": "oEmbed URL",
        "type": "string",
        "format": "uri",
        "contentMediaType": "application/oembed+json",
        "x-oembed-type": "video"
      },
      "width": {
        "title": "Video width",
        "type": "integer"
      },
      "height": {
        "title": "Video height",
        "type": "integer"
      },
      "title": {
        "title": "Video title",
        "type": "string"
      }
    }
  }
}

For documents, to display a link, we'd need a bit more than just the URI in the schema.json:

{
  "document": {
    "title": "document",
    "type": "object",
    "required": ["src"],
    "properties": {
      "src": {
        "title": "Document URL",
        "$ref": "json-schema-definitions://experience_builder.module/document-uri"
      },
      "title": {
        "title": "Document title",
        "type": "string"
      },
      "description": {
        "title": "Document description",
        "type": "string"
      },
      "filename": {
        "title": "Filename",
        "type": "string"
      },
      "filesize": {
        "title": "File size",
        "type": "integer",
        "description": "File size in bytes"
      },
      "mimetype": {
        "title": "MIME type",
        "type": "string"
      }
    },
    "document-uri": {
      "title": "Document URL",
      "type": "string",
      "format": "uri-reference",
      "pattern": "^(/|https?://)?.*\\.(txt|rtf|doc|docx|ppt|pptx|xls|xlsx|pdf|odf|odg|odp|ods|odt|fodt|fods|fodp|fodg|key|numbers|pages)(\\?.*)?(#.*)?$"
    }
  },
}