Add admin dashboard, Google Identity Service authentication & authorization, TCO calculation and other code changes

[abdulaziz-git]

• Change the update function and move it to the admin folder
• Define required variables configuration in the config.php file
• Implement Google Identity Services for admin Authentication
• Implement Google Identity Services for Authorization to Google Sheets API
• Implement PHP Sessions
• Add Admin Dashboard page
• Change from relative to an absolute path for files call
• Remove conf.php as it is not used anymore
• Use bootstrap 5.3.0 and Sweetalert2 for Admin Dashboard
• Manage config.json from the admin dashboard
• Deny direct access to the data folder
• Move dropdown options, and SVG icon to constants and clean some code
• Add the Total cost of ownership and sort the result by TCO or Upfront cost
• Fix TCO calculation, add Assumed filter lifetime options, change sorting function
• Move all defined variables to config.json and make database update available using update_key
• Change filter results to include no value of watts and filter cost
• Add buy now button analytics and change admin dashboard views