docs: add documentation for v1.8 (#3669)

docs/content/development/entities/overview.mdx

@@ -76,10 +76,10 @@ Developers can create custom entities in the Medusa backend, a plugin, or in a C
   {
     type: 'link',
     href: '/development/entities/create',
-    label: 'Create an Endpoint',
+    label: 'Create an Entity',
     customProps: {
       icon: Icons['academic-cap-solid'],
-      description: 'Learn how to create endpoints in Medusa.'
+      description: 'Learn how to create an entity in Medusa.'
     }
   },
   {
@@ -91,4 +91,22 @@ Developers can create custom entities in the Medusa backend, a plugin, or in a C
       description: 'Learn how to create migrations in Medusa.'
     }
   },
+  {
+    type: 'link',
+    href: '/development/entities/extend-entity',
+    label: 'Extend an Entity',
+    customProps: {
+      icon: Icons['academic-cap-solid'],
+      description: 'Learn how to extend a core Medusa entity.'
+    }
+  },
+  {
+    type: 'link',
+    href: '/development/entities/extend-repository',
+    label: 'Extend a Repository',
+    customProps: {
+      icon: Icons['academic-cap-solid'],
+      description: 'Learn how to extend a core Medusa repository.'
+    }
+  },
 ]} />