Add policies to the api based on oslo.policies.
Small changes in documentation. Provide generator for
sample policies file.
Add policies for agent and admin.
Story: 200112
Task: 4807
Depends-On: I76d737bf9d1216b041bc1a518cc2098f28e7da7b
Change-Id: Idf5c4ec1b663ad9ed3ab25744bdf0b7f28cdb1a2