Add feedback button functionality

[iamprathosh]

Fixes #495

Add feedback button functionality to the website's interface.

• App Component: Import and add the FeedbackButton component inside the MatomoProvider component in src/App.tsx.
• CSS Styling: Add styles for the .feedback-button class in src/app.css to position and style the feedback button.
• Feedback Button Component: Create a new FeedbackButton component in src/components/FeedbackButton.tsx that renders a floating button and opens a modal with a feedback form on click.
• Feedback Form Component: Create a new FeedbackForm component in src/components/FeedbackForm.tsx that renders a modal with a form for user feedback and handles form submission.

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