Add license "Policy" tab to 'License Compliance' page so that users can easily see existing license policies when viewing licenses - Provide the API to create a policy

Main issue - #14061 (closed)

This follows the sub issue convention described in gitlab-com/www-gitlab-com#4588 (closed).

• Provide the API to create a policy.

Details

This action can only be performed by someone with a maintainer role on the project.