Form Basics, Introfuction to Grid, Creating a Grid, Using Flexbox and Grid lessons: Remove additional resources and add assignment section

[carlosmperezm]

Because

It's part of the additional resources evaluation

This PR

• Remove the "Additional resources" section entirely from the following lessons:

  • Form Basics
  • Introduction to Grid
  • Creating a Grid
  • Using Flexbox and Grid

• To Introduction to Grid, add an assignment section with... no assignment! In the same vein as the assignment in Introduction to Flexbox.

Issue

Closes #30738

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide