new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/k8s.io/api/admissionregistration/v1alpha1/generated.proto

@@ -0,0 +1,108 @@
+/*
+Copyright 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.
+*/
+
+
+// This file was autogenerated by go-to-protobuf. Do not edit it manually!
+
+syntax = 'proto2';
+
+package k8s.io.api.admissionregistration.v1alpha1;
+
+import "k8s.io/apimachinery/pkg/apis/meta/v1/generated.proto";
+import "k8s.io/apimachinery/pkg/runtime/generated.proto";
+import "k8s.io/apimachinery/pkg/runtime/schema/generated.proto";
+import "k8s.io/apimachinery/pkg/util/intstr/generated.proto";
+
+// Package-wide variables from generator "generated".
+option go_package = "v1alpha1";
+
+// Initializer describes the name and the failure policy of an initializer, and
+// what resources it applies to.
+message Initializer {
+  // Name is the identifier of the initializer. It will be added to the
+  // object that needs to be initialized.
+  // Name should be fully qualified, e.g., alwayspullimages.kubernetes.io, where
+  // "alwayspullimages" is the name of the webhook, and kubernetes.io is the name
+  // of the organization.
+  // Required
+  optional string name = 1;
+
+  // Rules describes what resources/subresources the initializer cares about.
+  // The initializer cares about an operation if it matches _any_ Rule.
+  // Rule.Resources must not include subresources.
+  repeated Rule rules = 2;
+}
+
+// InitializerConfiguration describes the configuration of initializers.
+message InitializerConfiguration {
+  // Standard object metadata; More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata.
+  // +optional
+  optional k8s.io.apimachinery.pkg.apis.meta.v1.ObjectMeta metadata = 1;
+
+  // Initializers is a list of resources and their default initializers
+  // Order-sensitive.
+  // When merging multiple InitializerConfigurations, we sort the initializers
+  // from different InitializerConfigurations by the name of the
+  // InitializerConfigurations; the order of the initializers from the same
+  // InitializerConfiguration is preserved.
+  // +patchMergeKey=name
+  // +patchStrategy=merge
+  // +optional
+  repeated Initializer initializers = 2;
+}
+
+// InitializerConfigurationList is a list of InitializerConfiguration.
+message InitializerConfigurationList {
+  // Standard list metadata.
+  // More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#types-kinds
+  // +optional
+  optional k8s.io.apimachinery.pkg.apis.meta.v1.ListMeta metadata = 1;
+
+  // List of InitializerConfiguration.
+  repeated InitializerConfiguration items = 2;
+}
+
+// Rule is a tuple of APIGroups, APIVersion, and Resources.It is recommended
+// to make sure that all the tuple expansions are valid.
+message Rule {
+  // APIGroups is the API groups the resources belong to. '*' is all groups.
+  // If '*' is present, the length of the slice must be one.
+  // Required.
+  repeated string apiGroups = 1;
+
+  // APIVersions is the API versions the resources belong to. '*' is all versions.
+  // If '*' is present, the length of the slice must be one.
+  // Required.
+  repeated string apiVersions = 2;
+
+  // Resources is a list of resources this rule applies to.
+  // 
+  // For example:
+  // 'pods' means pods.
+  // 'pods/log' means the log subresource of pods.
+  // '*' means all resources, but not subresources.
+  // 'pods/*' means all subresources of pods.
+  // '*/scale' means all scale subresources.
+  // '*/*' means all resources and their subresources.
+  // 
+  // If wildcard is present, the validation rule will ensure resources do not
+  // overlap with each other.
+  // 
+  // Depending on the enclosing object, subresources might not be allowed.
+  // Required.
+  repeated string resources = 3;
+}
+