Backport EE API parameters in lib/api

What does this MR do?

This backports various EE API parameters to CE, ensuring the files changed are the same in both CE and EE.

EE MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10326

What are the relevant issue numbers?

• https://gitlab.com/gitlab-org/gitlab-ee/issues/9505
• https://gitlab.com/gitlab-org/gitlab-ee/issues/9970

TODO

• lib/api/group.rb
• lib/api/helpers/projects_helpers.rb
• lib/api/issues.rb
• lib/api/projects.rb
• lib/api/protected_branches.rb
• lib/api/settings.rb
• lib/api/users.rb
• lib/api/variables.rb

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides