Add attribute readonly inside embed/shared component in snippets

Summary

The component we use to render the embed and share URL for snippets is editable when it shouldn't. It doesn't have any impact if you edit it, but it should be read only.

Steps to reproduce

Browse a public snippet for example and click on the embed/share component, you'll be able to write there.

What is the expected correct behavior?

The component shouldn't be editable.