API to create group in an organization

Problem

We will need an API to create a group in an organization.

Requirements

• Should probably accept the same arguments as https://docs.gitlab.com/ee/api/groups.html#new-group
• Should accept an argument to specify which organization the group should be created in

Implementation plan

Modify the existing API such as https://docs.gitlab.com/ee/api/groups.html#new-group to create the group in the organization. Also, check the user creating the group belongs to the organization i.e. present in the organization_users table.