This commit adds docs and reno for migrating policies
into code [1].
Like oslo.config, with oslo.policy, we can define all of
default rules in code base and only change some rules
via policy file. Another thing that we should use yaml
format instead of json format.
[1] https://governance.openstack.org/tc/goals/queens/policy-in-code.html
Co-authored-By: Dai Dang-Van <daidv@vn.fujitsu.com>
Change-Id: I67984292022e2a92306b268a40861cff625c22c9
60d1627650