Add use_web_ide_extension_marketplace to user_pref

What does this MR do and why?

From the commit: Add use_web_ide_extension_marketplace to user_pref

• Also adds to GraphQL mutation
• Next commit will add feature flag and pass to Web IDE

Changelog: other

Context: This MR is part of enabling the Extension Marketplace for the Web IDE and supporting https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/289.

Screenshots or screen recordings

No visual change

How to set up and validate locally

1. Run `bin/rails db:migrate RAILS_ENV=development
2. Visit /-/graphql-explorer/ in your local GDK and run:

   mutation {
     userPreferencesUpdate(input:{ useWebIdeExtensionMarketplace: true }) {
       errors,
       userPreferences {
         useWebIdeExtensionMarketplace
       }
     }
   }

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.