[Bug]: Documentation for Rails is for Rails 6, but Rails is on Rails 7

### 💻

- [ ] Would you like to work on a fix?

### How are you using Babel?

babel-loader (webpack)

### Input code

n/a just documentation needs updating

### Configuration file name

_No response_

### Configuration

_No response_

### Current and expected behavior

I was reading the Rails instructions at https://babeljs.io/setup#installation and it mentions Rails 6, but Rails is now on Rails 7, so it should probably get updated. It also links to Webpacker, but Webpacker's site says "Webpacker has been retired" so I don't think these instructions are current.

### Environment

n/a, just documentation

### Possible solution

_No response_

### Additional context

_No response_

Start at the Rails instructions in the setup documentation at https://babeljs.io/setup#installation. Verify the current Rails version and the replacement for the retired Webpacker guidance, then update the instructions. Done means the page no longer refers to Rails 6 or directs readers to retired Webpacker documentation.

Written by the indexing model from the issue text.