Rewrite shimmer modal with dialog

[leoggonzalez]

There's a new html api to display Dialogs which has some native advantages like:

• Positioned by default
• :backdrop pseudo element that can be styled
• dom blocking by default when calling the native function modal.showModal

We should take advantages of this new element and rewrite our current implementation in shimmer.

There's already a react implementation in laic portal

** Acceptance criteria **

• Shimmer modal component implements html native dialog element