Feature Request: Add next.rubyui.com subdomain for Main Branch Preview

[cirdes]

Description

We need to set up a new subdomain: next.rubyui.com.
This subdomain should automatically deploy and stay in sync with the main branch of the RubyUI GitHub repository.
Its purpose is to serve as a “next” or “preview” environment showing the latest unreleased changes.

Additionally, the current production domain www.rubyui.com should remain synced with the latest RubyUI gem release published on RubyGems.org.

Goal

Prevent users who follow the official documentation from getting unexpected results due to instructions or features that have not yet been released.
By separating stable docs from “next” docs, we ensure reliability and avoid confusion.

[djalmaaraujo]

@cirdes What is missing here? Looks like https://next.rubyui.com/ is working. Should we write a step by step?