Feature: Add ActiveRecord Validations lesson

[JoshDevHub]

Because

There's a new lesson for the Rails course on validations added in this PR to the curriculum repo: https://github.com/TheOdinProject/curriculum/pull/27651

This PR

• Adds new lesson to the Rails course fixtures
• Runs db:seed task

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• [x] I have thoroughly read and understand The Odin Project Contributing Guide
• [x] The title of this PR follows the keyword: brief description of change format, using one of the following keywords:
  • Feature - adds new or amends existing user-facing behavior
  • Chore - changes that have no user-facing value, refactors, dependency bumps, etc
  • Fix - bug fixes
• [x] The Because section summarizes the reason for this PR
• [x] The This PR section has a bullet point list describing the changes in this PR
• [x] I have verified all tests and linters pass after making these changes.
• [ ] If this PR addresses an open issue, it is linked in the Issue section
• [ ] If applicable, this PR includes new or updated automated tests