refactor: add focus trap to modal component

[leMaur]

Summary

https://app.clickup.com/t/1je5e0d

When a modal is opened, the first focusable element should receive the focus. Tabbing should focus the next sibling and should keep the focus on elements in the modal.
When a modal is closed, the focus should come back to the element used to trigger the modal.
Saying that, this PR improves the modal component to take care of those behaviors.

Checklist

• I checked my UI changes against the design and there are no notable differences
• I checked my UI changes for any responsiveness issues
• I checked my (code) changes for obvious issues, debug statements and commented code
• I provided a screenshot of my changes to the component (if applicable)
• I regenerated the icons.html file and checked if my newly added icon is shown correctly (if necessary)
• I added an explanation on how to use the component to the readme (if necessary)
• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged