Add button "Post product" for admin. (#2)

* Add isAdmin property to User and Session, modify authOptions and env

This commit adds isAdmin property to User and Session interfaces, sets
isAdmin based on user email in authOptions, and introduces ADMIN and
SUPER_ADMIN variables in env for user role validation. The isAdmin
property is utilized for admin authentication check.

* Introduce Button component and utility functions

Added a Button component with variant handling and utility functions for class merging, currency formatting, relative date calculation, slug conversion, and admin role check.

* Add new dependencies including Radix UI themes in package-lock.json

Several new dependencies such as Radix UI themes and related packages have been included in the project to enhance UI functionality and styling options. This addition aims to improve the user interface and overall user experience of the application.

Author: Turskyi

Diff for: @types/next-auth.d.ts

@@ -4,6 +4,7 @@ declare module 'next-auth' {
   interface Session {
     user: {
       id: string;
+      isAdmin: boolean;
     } & DefaultSession['user'];
   }
 }