Merge pull request #54463 from saad-ali/volumeAttachmentAPI

Automatic merge from submit-queue. 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>.

Introduce new `VolumeAttachment` API Object

**What this PR does / why we need it**:

Introduce a new `VolumeAttachment` API Object. This object will be used by the CSI volume plugin to enable external attachers (see design [here](kubernetes/community#1258). In the future, existing volume plugins can be refactored to use this object as well.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*:  Part of issue kubernetes/enhancements#178

**Special notes for your reviewer**:
None

**Release note**:

```release-note
NONE
```

Kubernetes-commit: ebe8ea73fd1a961779242dfbb629befa153e96fc

storage/v1alpha1/BUILD

@@ -0,0 +1,42 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+filegroup(
+    name = "go_default_library_protos",
+    srcs = ["generated.proto"],
+    visibility = ["//visibility:public"],
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "doc.go",
+        "generated.pb.go",
+        "register.go",
+        "types.go",
+        "types_swagger_doc_generated.go",
+        "zz_generated.deepcopy.go",
+    ],
+    importpath = "k8s.io/api/storage/v1alpha1",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//vendor/github.com/gogo/protobuf/proto:go_default_library",
+        "//vendor/github.com/gogo/protobuf/sortkeys:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
+    ],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

storage/v1alpha1/doc.go

@@ -0,0 +1,20 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// +k8s:deepcopy-gen=package,register
+// +groupName=storage.k8s.io
+// +k8s:openapi-gen=true
+package v1alpha1 // import "k8s.io/api/storage/v1alpha1"