Feat: Add Blog Functionality to SaaS Starter

This pull request introduces a robust blog feature to the SaaS starter kit, allowing you to easily create and manage blog content within your SaaS application.

Key features

• Blog Listing and Individual Post Pages: Displays a list of all blog posts and dedicated pages for each individual post.
• MDX-based Content: Leverages MDX files for blog content, enabling you to write in Markdown with the flexibility to embed React components.
• Static Site Generation (SSG): Utilizes Next.js SSG capabilities to pre-render blog pages at build time, optimizing performance and SEO.

How to Add New Blog?

1. Create a MDX File: Add a new MDX file within the src/content/blog directory. The file name will determine the blog post slug.
2. Define Metadata: Include frontmatter at the beginning of your MDX file to specify metadata such as title, publication date, tags, and a brief description.

Metadata Format:

---
title: "Your Blog Post Title"
slug: "your-blog-post-slug"
publishedAt: "2023-11-29" 
readTime: "5 min"
tags: ["saas", "productivity"]
description: "A concise summary of your blog post"
tumbnail: "https://path/to/your/image.jpg" 
---

Your blog post content here...