allow passing custom fields

Author: eric-burel

docs/tutorialkit.dev/src/content/docs/reference/configuration.mdx

@@ -404,6 +404,28 @@ type TemplateType = "html" | "node" | "angular-cli" | "create-react-app" | "java
 
 ```
 
+##### `custom`
+
+Assign custom fields to a chapter/part/lesson.
+<PropertyTable inherited type="Record<string,any>" />
+
+This is useful when you want to consume items for the default `tutorial` collection
+in order to implement custom features.
+
+```yaml
+custom:
+  publishedAt: 2024-16-10
+  tags: tutorialkit,astro,vite
+```
+
+```ts
+import { getCollection } from 'astro:content';
+const collection = await getCollection('tutorial');
+for (const entry of collection) {
+  console.log("This part was published at:", entry.data?.custom?.publishedAt)
+}
+```
+
 ## Configure the Tutorialkit Astro integration
 
 `@tutorialkit/astro` is an integration for Astro. You can configure the integration in your `astro.config.ts` file.

packages/template/src/content/tutorial/1-basics/1-introduction/1-welcome/content.md

@@ -12,8 +12,11 @@ prepareCommands:
 terminal:
   panels: ['terminal', 'output']
 meta: 
-    description: "This is lesson 1"
-    image: "/logo.svg"
+  description: "This is lesson 1"
+  image: "/logo.svg"
+custom:
+  publishedAt: "2024-10-16"
+  
 ---
 
 # Kitchen Sink [Heading 1]

packages/types/src/entities/index.ts

@@ -1,5 +1,5 @@
 import type { I18nSchema } from '../schemas/i18n.js';
-import type { ChapterSchema, LessonSchema, PartSchema } from '../schemas/index.js';
+import type { ChapterSchema, CustomSchema, LessonSchema, PartSchema } from '../schemas/index.js';
 import type { MetaTagsSchema } from '../schemas/metatags.js';
 
 export type * from './nav.js';
@@ -60,6 +60,8 @@ export type I18n = Required<NonNullable<I18nSchema>>;
 
 export type MetaTagsConfig = MetaTagsSchema;
 
+export type CustomConfig = CustomSchema;
+
 export interface Tutorial {
   logoLink?: string;
   firstPartId?: string;

packages/types/src/schemas/common.ts

@@ -203,13 +203,18 @@ export const editorSchema = z.union([
   }),
 ]);
 
+const customSchema = z.record(z.string(), z.any());
+
 export type TerminalPanelType = z.infer<typeof panelTypeSchema>;
 export type TerminalSchema = z.infer<typeof terminalSchema>;
 export type EditorSchema = z.infer<typeof editorSchema>;
+export type CustomSchema = z.infer<typeof customSchema>;
 
 export const webcontainerSchema = commandsSchema.extend({
   meta: metaTagsSchema.optional(),
 
+  custom: customSchema.optional(),
+
   previews: previewSchema
     .optional()
     .describe(