Only show permitted projects

The drop-down list of projects shown on the https://gitbox.apache.org/boxer/?action=newrepo page includes all possible projects.

This makes it tedious to select the desired project.
I realise that one can type the first letter of the name, but that does not help if one has access to two projects with the same first letter (especially if that is 's', as there are lots of them)

It would be a lot easier for users if the list only showed projects to which they have access.

Start at the new-repository page at https://gitbox.apache.org/boxer/?action=newrepo and trace how its project dropdown is populated and how the current user's access is determined. Done means the list contains only projects the user can access, including when project names share their first letter.

Written by the indexing model from the issue text.