Site Migration: Improve the Dead-end on the do-it-for-me migration flow

[valterlorran]

More context: paYKcK-4Wf-p2

The users now have the option to select the assisted migration right up-front on a new step we introduced on #91856. However, they reach a dead-end step with the instructions for the next steps, which may take a few days to complete.

We should provide options on this instruction step to help the users get familiar with our tools or maybe introduce them to some learning content.