Support `config/vite.rb` for advanced configuration

[ElMassimo]

Background 📜

Currently, there are two main ways to configure Vite Ruby:

• a shared config/vite.json file
• override settings using environment variables

Feature Request ✨

Adding support for an optional config/vite.rb file that is called when resolving the configuration would make it easier to configure ViteRuby.env as needed regardless of how Vite Ruby is executed (rake task, binstub, or bundle exec).

Documentation 📖

Since any configuration in this ruby file can not be read when invoking the node vite executable directly, this would be regarded an advanced feature, and config/vite.rb would not be added during installation.

[ElMassimo]

Released in vite_ruby@3.0.6, and it's now documented in the Config section.