[goal] Deprecate the JSON formatted policy file

As per the community goal of migrating the policy file
the format from JSON to YAML[1], we need to do two things:

1. Change the default value of '[oslo_policy] policy_file''
config option from 'policy.json' to 'policy.yaml' with
upgrade checks.

2. Deprecate the JSON formatted policy file on the project side
via warning in doc and releasenotes.

Also replace policy.json to policy.yaml ref from doc and tests.

[1]https://governance.openstack.org/tc/goals/selected/wallaby/migrate-policy-format-from-json-to-yaml.html

Change-Id: I6fc6f7d95e4efde6ea3bd0f1e4134aa54ce3889a

lower-constraints.txt

@@ -64,23 +64,23 @@ os-service-types==1.7.0
 osc-lib==1.10.0
 oslo.cache==1.29.0
 oslo.concurrency==3.26.0
-oslo.config==5.2.0
-oslo.context==2.19.2
+oslo.config==6.8.0
+oslo.context==2.22.0
 oslo.db==5.0.0
 oslo.i18n==3.20.0
 oslo.log==3.36.0
 oslo.messaging==9.3.0
 oslo.middleware==3.31.0
-oslo.policy==1.30.0
+oslo.policy==3.6.0
 oslo.reports==1.18.0
 oslo.rootwrap==5.8.0
 oslo.serialization==2.18.0
 oslo.service==1.24.0
-oslo.upgradecheck==0.1.0
-oslo.utils==3.33.0
+oslo.upgradecheck==1.3.0
+oslo.utils==4.5.0
 oslo.versionedobjects==1.33.3
 oslotest==3.2.0
-packaging==17.1
+packaging==20.4
 paramiko==2.7.1
 Paste==2.0.2
 PasteDeploy==1.5.0
@@ -121,7 +121,7 @@ requests==2.20.0
 requests-mock==1.2.0
 requestsexceptions==1.4.0
 restructuredtext-lint==1.1.3
-rfc3986==1.1.0
+rfc3986==1.2.0
 Routes==2.3.1
 rsa==3.4.2
 setuptools==21.0.0