add-project.py: Pagination, phase 1

get_trusted_runners:
Pass iterator=True to project.runners.list to ensure that it
paginates through all results.

get_projects_for_runner:
Request pagination information when retrieving the list of projects.
Use this information to ensure we error out if we retrieved
incomplete information (instead of acting on the information as if
it were complete). Reformatted the query string in the process to
hopefully make it more readable.

I did not implement pagination for the graphql query.