Move GitHub issue validation to Repository step

While configuring a new project, if the user faces any sort of GitHub issue, the issue will be highlighted on the last step (Review). And the the user will have to go all the way back to the Repository step where they configured the repo for the new project. Instead, all GitHub issues must be highlighted directly on the Repository step so that the user doesn't have to jump between steps. 

New-project wizard: GitHub create/initialize now runs on Repository's Next (and step headers); errors show on the row there. Quick gate + tests green; visual check done (desktop+448px). PR #7769 merged; deploy superseded. Deferred: existing-repo access pre-check. Memory: used mem-25288.