Add Rails update guidelines

What does this MR do and why?

This MR is inspired by !68955 (merged) and aims to provide some guidance for updating Rails.

It includes:

• A new documentation section Rails update guidelines
• A bash script scripts/rails-update-bisect that helps to use git bisect with a local rails repository.

Preview: http://main-ee-70778.178.62.207.141.nip.io/ee/development/rails_update.html

Screenshots or screen recordings

https://asciinema.org/a/437128

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.