refactor: replace postSlug with Astro content slug

* refactor: replace postSlug with Astro content slug

Remove postSlug from blog schema. Refactor articles that use postSlug. Remove slugify function from slugify util file. Replace slugify logic with Astro's content collections slug logic.

Closes: #186

* docs: update docs for removed slugify contents

* refactor: remove unused import

src/pages/search.astro

@@ -11,10 +11,11 @@ import SearchBar from "@components/Search";
 const posts = await getCollection("blog", ({ data }) => !data.draft);
 
 // List of items to search in
-const searchList = posts.map(({ data }) => ({
+const searchList = posts.map(({ data, slug }) => ({
   title: data.title,
   description: data.description,
   data,
+  slug,
 }));
 ---