feat: Update Landing page background Image

[Chifez]

What does this PR do?

This PR allows the user to do the following

• change the default background image of the landing page
• hide or show the background image

Fixes #467

https://github.com/user-attachments/assets/523ee0c1-c509-41ca-b4a0-d8d2a7db6df2

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] Chore (refactoring code, technical debt, workflow improvements)
• [x] Enhancement (small improvements)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change adds a new database migration
• [ ] This change requires a documentation update

How should this be tested?

• run on localhost

Checklist

Required

• [x] Filled out the "How to test" section in this PR
• [ ] Self-reviewed my own code
• [ ] Commented on my code in hard-to-understand bits
• [ ] Ran pnpm build
• [ ] Checked for warnings, there are none
• [ ] Removed all console.logs
• [ ] Merged the latest changes from main onto my branch with git pull origin main
• [ ] My changes don't cause any responsiveness issues

Appreciated

• [ ] If a UI change was made: Added a screen recording or screenshots to this PR
• [ ] Updated the ClassroomIO Docs if changes were necessary