feat(techdocs-node): accept sequence node custom tags

This change to the MKDOCS_SCHEMA lets the validation logic accept
custom tags that are sequence nodes as valid.

Signed-off-by: Viktor Bahr <viktor.bahr@tier.app>

plugins/techdocs-node/src/stages/generate/helpers.ts

@@ -134,6 +134,14 @@ export const MKDOCS_SCHEMA = DEFAULT_SCHEMA.extend([
     instanceOf: UnknownTag,
     construct: (data: string, type?: string) => new UnknownTag(data, type),
   }),
+  new Type('', {
+    kind: 'sequence',
+    multi: true,
+    representName: o => (o as UnknownTag).type,
+    represent: o => (o as UnknownTag).data ?? '',
+    instanceOf: UnknownTag,
+    construct: (data: string, type?: string) => new UnknownTag(data, type),
+  }),
 ]);
 
 /**