Moves empty state instructions on MLflow usage to a modal

What does this MR do and why?

Moves instructions on MLflow usage to a modal

Empty state for model registry was too busy, so the code instructions
were moved to a modal, which can be openened both from the empty state
and from a button on the overflow menu that used to only copy the url.

Screenshots or screen recordings

Before	After
	2024-05-29_16.13.36

How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:model_registry)

2. Open any project, then navigate to Deploy > Model registry.

Related to #456437 (closed)