feat: testimonial carousel on homepage

[mountainmort]

Description

• Refactored existing Testimonials into a JSON object with capability to retrieve testimonials by Name, ID, or retrieve all Testimonials.
• Created TestimonialCard component based on the testimonial divs that existed on the Testimonials page.
• Updated the Testimonial page to pull all testimonials from the new Testimonials utility and use the TestimonialCard component.
• Refactored the Testimonial on the Donate page to use the new retrieve testimonial by Name endpoint and TestimonialCard.
• Created a TestimonialCarousel component that allows scrolling through all available Testimonials, and embedded this on the home page.
  • Note: I used nuka-carousel here as this library was already in the project and used for the SponsorSlider component.

Related Issue

https://github.com/Vets-Who-Code/vets-who-code-app/issues/466

Motivation and Context

The big dog requested it get done, so it got done.

How Has This Been Tested?

• Verified pages that were updated remain the same (Testimonials, Donate)
• Verified Home page works with across our different size screens and independent of theme
• Tests are passing

Screenshots (if appropriate):

1. Home Page with carousel - light mode / desktop

2. Home Page with carousel - dark mode / desktop

3. Home Page with carousel - light mode / mobile

4. Home Page with carousel - dark mode / mobile

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

I'd be interested in getting some feedback here on what unit tests I should/could include.

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