List github packages on the "submit package" page

If the user has a github account, we could list the packages he has access to, and those of orgas too.

Having the ability to add the service hook automatically would be really cool, but not sure how much work that is.

Start at the submit package page and inspect how the application connects a user's GitHub account and handles package submission. Determine the scope for listing accessible personal and organization packages, then assess the separate service-hook automation idea. Done means the agreed package list is available on the page and the submission flow works for those packages.

Written by the indexing model from the issue text.