Resolve "Include new API endpoints in e2e test"

Overview

This MR covers adding additional endpoints to the e2e tests and improved formatting of the diff reports. This is primarily focusing on the various get_all_* wrapper functions in gitlab/api.

Tasks

• Update README.md if needed
• Add delayed import retry for failed imports due to rate limiting (line 264 in congregate/migration/gitlab/importexport.py):

project_import:
  { threshold: 30,
    interval: 10.minutes },

Closes #258 (closed)