Merge pull request #59293 from roycaihw/openapi_endpoint

Automatic merge from submit-queue (batch tested with PRs 60011, 59256, 59293, 60328, 60367). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Serve OpenAPI spec with single /openapi/v2 endpoint

**What this PR does / why we need it**:
We are deprecating format-separated endpoints (`/swagger.json`, `/swagger-2.0.0.json`, `/swagger-2.0.0.pb-v1`, `/swagger-2.0.0.pb-v1.gz`) for OpenAPI spec, and switching to a single `/openapi/v2` endpoint in Kubernetes 1.10. The design doc and deprecation process are tracked at: https://docs.google.com/document/d/19lEqE9lc4yHJ3WJAJxS_G7TcORIJXGHyq3wpwcH28nU

Requested format is specified by setting HTTP headers

header | possible values
-- | --
Accept | `application/json`, `application/com.github.proto-openapi.spec.v2@v1.0+protobuf`
Accept-Encoding | `gzip`

This PR changes dynamic_client (and kubectl as a result) to use the new endpoint. The old endpoints will remain in 1.10 and 1.11, and get removed in 1.12. 

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
action required: Deprecate format-separated endpoints for OpenAPI spec. Please use single `/openapi/v2` endpoint instead.
```

/sig api-machinery

plugin/pkg/auth/authorizer/rbac/bootstrappolicy/policy.go

@@ -176,6 +176,7 @@ func ClusterRoles() []rbac.ClusterRole {
 					// do not expand this pattern for openapi discovery docs
 					// move to a single openapi endpoint that takes accept/accept-encoding headers
 					"/swagger.json", "/swagger-2.0.0.pb-v1",
+					"/openapi", "/openapi/*",
 					"/api", "/api/*",
 					"/apis", "/apis/*",
 				).RuleOrDie(),

plugin/pkg/auth/authorizer/rbac/bootstrappolicy/testdata/cluster-roles.yaml

@@ -635,6 +635,8 @@ items:
     - /apis
     - /apis/*
     - /healthz
+    - /openapi
+    - /openapi/*
     - /swagger-2.0.0.pb-v1
     - /swagger.json
     - /swaggerapi