Paginate all endpoints that return an array

changelogs/unreleased/paginate-all-the-things.yml

lib/api/award_emoji.rb

lib/api/boards.rb

lib/api/branches.rb

lib/api/deploy_keys.rb

lib/api/files.rb

lib/api/helpers/pagination.rb

lib/api/labels.rb

lib/api/merge_request_diffs.rb

lib/api/merge_requests.rb

lib/api/pagination_params.rb

lib/api/project_hooks.rb

lib/api/repositories.rb

lib/api/system_hooks.rb

lib/api/tags.rb

lib/api/templates.rb

lib/api/users.rb

spec/requests/api/branches_spec.rb

spec/requests/api/merge_requests_spec.rb

spec/requests/api/milestones_spec.rb