feat: Add PostsController and configure routes

- Added a new file `PostsController.php` in the `app/Http/Controllers` directory.
- Implemented the `index()` method to retrieve all posts using the Sheets facade.
- Implemented the `show()` method to display a single post using route model binding with Sheets.
- Updated the `RouteServiceProvider.php` file to bind the 'post' route parameter to retrieve posts from the Sheets collection.
- Created a new configuration file `sheets.php` in the `config` directory, defining default settings for collections and their corresponding sheet classes, path parsers, content parsers, and extensions.
- Added a new markdown file `hello-world.md` in the `content/posts` directory as an example post.
- Created two new blade view files: `index.blade.php` and `show.blade.php`, under the `resources/views/posts` directory, for displaying lists of posts and individual post details respectively.
- Modified the existing web routes (`web.php`) to include routes for accessing posts.

The changes enable users to view all posts on `/posts`, as well as access individual post details at `/post/{post}`.

app/Http/Controllers/PostsController.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use Spatie\Sheets\Facades\Sheets;
+use Spatie\Sheets\Sheet;
+
+class PostsController extends Controller
+{
+    public function index()
+    {
+        $posts = Sheets::all();
+        
+        return view('posts.index', compact('posts'));
+    }
+
+    public function show(Sheet $post)
+    {
+        dd($post);
+        return view('posts.show', compact('post'));
+    }
+}