feat: new element for paper's own widgets (#528)

* feat: new element for paper's own widgets

* rename type

* fix typo

* Update stroeer/core/v1/article.proto

Co-authored-by: Patrick Dahms <pat.dahms@googlemail.com>

* format comment

---------

Co-authored-by: Jan Meischner <jan.meischner@stroeer.de>
Co-authored-by: Jan Meischner <jan.meischner@googlemail.com>
Co-authored-by: Patrick Dahms <pat.dahms@googlemail.com>

stroeer/core/v1/article.proto

@@ -270,6 +270,7 @@ message Article {
      * | `AGENCY`               | author, contains one `metadata` [`Asset`][a]                                                                 |
      * | `EDGE_SIDE_INCLUDE`    | `<esi:include>` that must be resolved server-side for SEO reasons, otherwise similar to `OEMBED`             |
      * | `CITATION`             | oEmbed, contains one `metadata` [`Asset`][a]. Todo: sample                                                   |
+     * | `INTERNAL_WIDGET`      | widget or embed that is handled directly by the front end rendering Todo: sample                             |
      *
      * [a]: article_%DB%B0_element_%DB%B0_asset.html
      * [e]: #element
@@ -291,6 +292,7 @@ message Article {
       AGENCY = 7;
       EDGE_SIDE_INCLUDE = 8;
       CITATION = 9;
+      INTERNAL_WIDGET = 10;
     }
     /** @CodeBlockEnd */