fix(oxhugo): Do not discard embedded HTML

In 'processors/parse.ts' the 'remarkRehype' plugin is used with
'allowDangerousHtml' enabled, but that needs to be combined with (e.g.)
'rehypeRaw' to have any effect on the output.

quartz/plugins/transformers/oxhugofm.ts

@@ -1,4 +1,6 @@
 import { QuartzTransformerPlugin } from "../types"
+import rehypeRaw from "rehype-raw"
+import { PluggableList } from "unified"
 
 export interface Options {
   /** Replace {{ relref }} with quartz wikilinks []() */
@@ -102,5 +104,9 @@ export const OxHugoFlavouredMarkdown: QuartzTransformerPlugin<Partial<Options>>
       }
       return src
     },
+    htmlPlugins() {
+      const plugins: PluggableList = [rehypeRaw]
+      return plugins
+    },
   }
 }