[Feature Request] New CBR policy sdk supported

[Lance52259]

What this PR does / why we need it:
According to existing demands, it is now necessary to support CBR policy related interface functions.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged):

NONE

Special notes for your reviewer:

Release note:

1. new CBR policy sdk supported
2. new sdk test supported

Acceptance Steps Performed

go test -v -run Test=== RUN   TestCreateV3PolicyMarshall
--- PASS: TestCreateV3PolicyMarshall (0.00s)
=== RUN   TestCreateV3Policy
--- PASS: TestCreateV3Policy (0.00s)
=== RUN   TestDeleteV3Policy
--- PASS: TestDeleteV3Policy (0.00s)
=== RUN   TestUpdateV3Policy
--- PASS: TestUpdateV3Policy (0.00s)
PASS
ok      github.com/huaweicloud/golangsdk/openstack/cbr/v3/policies/testing      0.014s

[coveralls]

Pull Request Test Coverage Report for Build 1280

• 62 of 78 (79.49%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 68.295%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
openstack/cbr/v3/policies/results.go	13	19	68.42%
openstack/cbr/v3/policies/requests.go	43	53	81.13%

Totals
Change from base Build 1276:	0.05%
Covered Lines:	11729
Relevant Lines:	17174

---

💛 - Coveralls