Add a manual Retry button to new repo creation flow

[BenEmdon]

Enhancement ✨

Add a manual retry button to the setupv2.html.erb so that if enough goes wrong, a student has the option to perform a manual retry.

This is useful when importing starter code fails but repo creation passes (since importing starter code is observed from PorterStatusJob but not retried).

In response to the post PR tasks in #1385